for the variable A type the word lambda, fory type the word gamma, otherwise treat these as you would any other variable We will solve the heat equation -6, 0

Answers

Answer 1

The required heat equation is u(x, t) = (A×cos(λx) + B×sin(λx)) × exp(-λ²t)

To solve the heat equation in the given interval [-6, 0], we can use the separation of variables method. Let's denote the dependent variable as u(x, t), where x represents the spatial variable and t represents the temporal variable.

The heat equation in one dimension is given by:

∂u/∂t = α ∂²u/∂x²,

where α is the thermal diffusivity constant.

To solve this equation, we assume that the solution can be represented as a product of two functions, each depending on a single variable:

u(x, t) = X(x)T(t).

Substituting this into the heat equation, we have:

X(x)T'(t) = αX''(x)T(t),

where prime (') denotes differentiation with respect to the variable.

Dividing both sides by αX(x)T(t), we get:

T'(t)/T(t) = αX''(x)/X(x).

Since the left side depends only on t and the right side depends only on x, both sides must be equal to a constant, which we'll denote as -λ²:

T'(t)/T(t) = -λ² = αX''(x)/X(x).

Now, let's solve the temporal part of the equation:

T'(t)/T(t) = -λ²

This is a separable ordinary differential equation (ODE), and its general solution is given by:

T(t) = exp(-λ²t).

Next, let's solve the spatial part of the equation:

αX''(x)/X(x) = -λ².

This is also a separable ODE, and its general solution is given by:

X(x) = A×cos(λx) + B×sin(λx),

where A and B are arbitrary constants.

Therefore, the general solution to the heat equation is:

u(x, t) = (A×cos(λx) + B×sin(λx)) × exp(-λ²t).

Since we have the given interval [-6, 0], we can apply appropriate boundary conditions to determine the values of A, B, and λ that satisfy the problem.

To learn more about heat equation: https://brainly.com/question/13415835

#SPJ11


Related Questions

A triangle has side lengths of (10x+7y)(10x+7y) centimeters, (3x+3z)(3x+3z) centimeters, and (8z+10y)(8z+10y) centimeters. Which expression represents the perimeter, in centimeters, of the triangle?

Answers

Answer:

(109x²+140xy+18xz+49y²+160yz+73z²) centimeters

Step-by-step explanation:

perimeter = sum of all sides

side A = (10x+7y)(10x+7y)

= 100x² +70xy +70xy +49y²

= (100x² +140xy +49y²) centimeters

side B = (3x+3z)(3x+3z)

= 9x² +9xz +9xz +9z²

= (9x² +18xz +9z²) centimeters

side C = (8z+10y)(8z+10y)

= 64z² +80yz +80yz +100y²

= (64z² +160yz +100y²) centimeters

Perimeter = 100x²+140xy+49y² + 9x²+18xz+9z² + 64z²+160yz+100y²

collect like terms

= 100x² +9x²+140xy+18xz+49y²+160yz+9z²+64z²

= (109x²+140xy+18xz+49y²+160yz+73z²) centimeters

Answer: 13x+17y+11z

Step-by-step explanation:

A coach is buying snacks for 22 players at a soccer match. She pays a total of $77 to
buy each player a bottle of water and an energy bar. The price of one energy bar is $2.
Let w equal the price of a bottle of water. Write an equation that
represents the situation.

Answers

Answer: 22( w + 2 ) =77 and the amount of the water bottle would be 1.50

Step-by-step explanation: i dont know what to write??

Serenity filled up her car with gas before embarking on a road trip across the country. Let � G represent the number of gallons of gas remaining in her gas tank after driving for � t hours. A graph of � G is shown below. Write an equation for � G then state the � y-intercept of the graph and determine its interpretation in the context of the problem.

Answers

The equation is: G = -⁵/₄t + 15

The slope of the function represents that ⁵/₄ gallons of gas is consumed to drive the car for one hour.

How to find the linear equation of the graph?

The formula for the equation of a line in slope intercept form is:

y = mx + c

where:

m is slope

c is y-intercept

From the graph, we see that:

y-intercept = 15 gallons

Now, the slope is gotten from the formula:

Slope = (y₂ - y₁)/(x₂ - x₁)

Slope = (10 - 5)/(4 - 8)

Slope = -⁵/₄

Thus, equation is:

G = -⁵/₄t + 15

The slope of the function represents that ⁵/₄ gallons of gas is consumed to drive the car for one hour.

Read more about Linear equation graph at: https://brainly.com/question/28732353

#SPJ1

Serenity filled up her car with gas before embarking on a road trip across the country. Let G represent

A rectangle has a height oft2+7t+6t2+7t+6t, squared, plus, 7, t, plus, 6 and a width of2t+12t

Answers

The area of the rectangle with a height of t² + 7t + 6 and a width of 2t + 1 is given by the expression 2t³ + 15t² + 19t + 6.

To find the area of the rectangle, we need to multiply the height by the width.

Given:

Height = t² + 7t + 6

Width = 2t + 1

Area = Height * Width

Substituting the given values:

Area = (t² + 7t + 6) * (2t + 1)

Expanding the expression:

Area = 2t * t² + 2t * 7t + 2t * 6 + 1 * t² + 1 * 7t + 1 * 6

Area = 2t³ + 14t² + 12t + t² + 7t + 6

Combining like terms:

Area = 2t³ + 15t² + 19t + 6

Therefore, the area of the rectangle with a height of t² + 7t + 6 and a width of 2t + 1 is given by the expression 2t³ + 15t² + 19t + 6.

Learn more about Area of rectangle here

https://brainly.com/question/29945663

#SPJ4

Given question is incomplete, the complete question is below

What is the area of a rectangle with a height of t² + 7t + 6 and a width of 2t + 1

Write 3g as a percentage of 20g​

Answers

Answer:

15%

Step-by-step explanation:

3÷20=0.15

0.15×100=15

Lily and nada share silver coins in the ratio 7:3. if lily gives 3 silver coins to nada, the ratio becomes 5:3. how many silver coins did lily have initially?

Answers

The number of silver coins Lily initially had is 28.

What is ratios?

A ratio is described as a comparing two quantities with the same unit to determine the amount of each quantity is existent in the other. Ratios are divided into two types.

The first is a part-to-part ratio, and the second is a part-to-whole ratio. The part-to-part ratio expresses the relationship between 2 separate entities or groups.

Now according to the question;

Let 'x' be the share of silver coin of Lily.

Let 'y' be the share of silver coin of Nada.

Lily and Nada share silver coins in the ratio 7:3

Thus, x/y = 7/3

Cross-multiplying

3x = 7y (equation 1)

Now, if Lily gives 3 silver coins to Nada, the ratio becomes 5:3.

(x - 3)/(y + 3) = 5/3

cross multiplying;

3x - 9 = 5y + 15

Simplifying;

3x  = 5y + 24 (equation 2)

Comparing equation 1 and 2.

7y = 5y + 24

2y = 24

y = 12 (Nada's share)

Substitute the value of y in equation 1;

3x = 7y

3x = 7×12

x = 28

Therefore, the initial share if Lily was 28.

To know more about the ratios, here

https://brainly.com/question/2914376

#SPJ4

The algebra teacher said if you square my age then subtract 23 times my age, the result is 50. How old is he?

Answers

Answer:

25

Step-by-step explanation:

The algebra teacher said if you square my age then subtract 23 times my age, the result is 50. How old

Answer:

She is 25

Step-by-step explanation:

25^2 = 625

23*25 = 575

625 - 575 = 50

See attached picture, is there a way to enter equations or algebraic symbols?

See attached picture, is there a way to enter equations or algebraic symbols?

Answers

SOLUTIONS

Solve a given equations or algebraic symbols?

\(\begin{gathered} f(x)=x^2+2x \\ g(x)=1-x^2 \end{gathered}\)

(A)

\(\begin{gathered} (f+g)(x)=(x^2+2x)+(1-x^2) \\ collect\text{ like terms} \\ x^2-x^2+2x+1 \\ (f+g)(x^)=2x+1 \end{gathered}\)

(B)

\(\begin{gathered} (f-g)(x)=(x^2+2x)-(1-x^2) \\ =x^2+2x-1+x^2 \\ =x^2+x^2+2x-1 \\ (f-g)(x)=2x^2+2x-1 \end{gathered}\)

(C)

\(\begin{gathered} fg(x)=(x^2+2x)(1-x^2) \\ =x^2-x^4+2x-2x^3 \\ fg(x)=-x^4-2x^3+x^2+2x \end{gathered}\)

(D)

\(\begin{gathered} \frac{f}{g}(x)=(x^2+2x)\div(1-x^2) \\ =\frac{x^2+2x}{1-x^2} \end{gathered}\)

kayla has a deck that measures 4 feet by 21 feet. she wants to increase each dimension by equal lengths so that the area is doubled. how much should she increase each dimension?

Answers

Answer:

Increase by 3.

Step-by-step explanation:

4 x 21 = 84

84 x 2 = 168

Begin to try numbers.

5 x 22 = 110

6 x 23 = 138

7 x 24 = 168

7 - 4 = 3

24 - 21 = 3

Increase each side by 3 ft. for a total dimension of 7 ft. x 24 ft.

A card is drawn from a well shuffled deck of 52 cards. Find P (drawing a face card or a 4). A face card is a king queen of jack

Answers

Answer:

The probability of drawing a face card or a 4 is approximately 0.2885, or 28.85%.

Step-by-step explanation:

To find the probability of drawing a face card or a 4 from a well shuffled deck of 52 cards, we need to count the number of cards that are either a face card or a 4, and divide that number by the total number of cards in the deck.

There are 12 face cards in a deck (4 kings, 4 queens, and 4 jacks) and 4 cards with the number 4, but the card with 4 is also a face card (the four of hearts), so we need to subtract one card from the total. Therefore, there are 15 cards in the deck that are either a face card or a 4.

The total number of cards in the deck is 52. Therefore, the probability of drawing a face card or a 4 from a well shuffled deck of cards is:

P = number of desired outcomes / total number of possible outcomes P = 15/52 P = 0.2885 (rounded to four decimal places)

So the probability of drawing a face card or a 4 is approximately 0.2885, or 28.85%.

brainliest Plssss

how do I solve this? 4-0,9+(-0,11)-(-1,3)

Answers

Answer:

Hope it will help a lot ask for more info

how do I solve this? 4-0,9+(-0,11)-(-1,3)

b) The average age of Kishan and Dolma is 15 years and that of Dolma and Shashwat is 14 years. If Kishan is 17 years old, find the age of Dolma and Shashwat.​

Answers

Step-by-step explanation:

average means the sum of all values divided by a number of values

b) The average age of Kishan and Dolma is 15 years and that of Dolma and Shashwat is 14 years. If Kishan

HELP MEEEEEEEE PLEASE

HELP MEEEEEEEE PLEASE

Answers

Answer:

Option A (3/4)

Step-by-step explanation:

Please mark Brainliest

Answer:

THATS CORREC T

Step-by-step explanation:

CAUSE A IS THE RIGHT ONE THE REST BIS WRONG BUT IT CAN E CONFUSING

I’d really appreciate if you’d also give a brief explanation:)

Id really appreciate if youd also give a brief explanation:)

Answers

Answer:

Only area of PQR can be calculated.

Step-by-step explanation:

In PQR, we have both the base (24 cm) and the height (15cm) which is perpendicular to the base. Therefore using these two measurements, we can take

\( \frac{1}{2} \times 24 \times 15\)

This is equal to 180 cm².

Calculate the derivative of the following function. y=(secx+tanx) 12
dx
dy

=12(sec(x)+tan(x)) 11
(sec(x)tan(x)+sec 2
(x)) a. Use implicit differentiation to find dx
dy

. b. Find the slope of the curve at the given point. 9xy=3;(1, 3
1

) a. dx
dy

=− x
y

b. The slope at (1, 3
1

) is − 3
1

.

Answers

Given function:y = (sec x + tan x)12

On taking the derivative of y with respect to x, we get:dy/dx = d/dx(sec x + tan x)12

Use chain rule,dy/dx

= 12(sec x + tan x)11(d/dx(sec x + tan x)

Now, d/dx(sec x + tan x) can be written asd/dx(sec x + sin x/cos x)

= sec x tan x + sec² xWe get,dy/dx

= 12(sec x + tan x)11 (sec x tan x + sec² x)

Therefore, dy/dx = 12(sec x tan x + sec² x)(sec x + tan x)11

Now, let us solve for part a) of the question using implicit differentiation:9xy = 3

Taking the derivative of both sides with respect to x, we get:9(d/dx)(xy)

= (d/dx)3

Taking the derivative of xy with respect to x, we get:xy + x(dy/dx)y = 0

On substituting this value in the above equation, we get:9(xy + x(dy/dx)y)

= 0dy/dx

= -(9xy)/(xy)

= -9/1

= -9

Thus, the value of dx/dy is -9.

Now, let us solve for part b) of the question:9xy = 3

Let us first differentiate this expression with respect to x:9(d/dx)(xy)

= (d/dx)3xy + x(dy/dx)y

= 3y + x(dy/dx)Y

Substituting the value of dy/dx, we get:xy = 1

Solving these two equations for x = 1 and

y = 3,

we get:xy = 3

Now, the slope of the curve at point (1, 31) is given by:dy/dx = - x/y

= -1/3

Thus, the slope of the curve at point (1, 31) is -31.

To know more about slope visit :-

https://brainly.com/question/16949303

#SPJ11

Answer this for 20 POINTS

Answer this for 20 POINTS

Answers

Answer: C

Step-by-step explanation: im sorry if its wrong creati deleted all my points and im at -92 points

In March, Delphine's house had 40\%40%40, percent more snowfall than in February. Delphine's house had fff centimeters of snowfall in February.
Which of the following expressions could represent how much snowfall Delphine had at her house in March?
Choose 2 answers:
Choose 2 answers:

(Choice A)
A
40f40f40, f

(Choice B)
B
40+f40+f40, plus, f

(Choice C)
C
1.4f1.4f1, point, 4, f

(Choice D)
D
40f+f40f+f40, f, plus, f

(Choice E)
E
\dfrac4{10}f+f
10
4

f+f

Answers

2.4 f of snow would fall in March.

How to find centimeters of snowfall in February?

Given that

Delphine's home received 40% 40% 40% 40% more snowfall in March compared to February.

now find the Delphine's house had fff centimeters of snowfall in February.

Let f represent the volume of snow that fell in February.

If there is 40% more snowfall in February than there was in March,

Consequently, the snowfall would be

\(f+( \frac{100+40}{100} )f\)

\(f+( \frac{140}{100} )f\)

f + 1.4f

2.4f

Therefore, 2.4f of snow would fall in march.

learn more about equations from here:

https://brainly.com/question/2972832

#SPJ9

HURRY I WILL GIVE U BRAINLYIST Renaissance artists learned about depth and ______, which they incorporated in their works of art.

perspective

shading

color

shapes

Answers

Answer:

persepctive

Step-by-step explanation:

have a great day<3

Perspective im pretty sure

Solve.
10⁵
pls help meh​

Solve. 10pls help meh

Answers

Answer:

100000

Step-by-step explanation:

10 x 10 x 10 x 10 x 10

10x10x10x10x10=100,000

if there is 1$ in taxes on 25$ worth of clothing, what percent is paid for the 25$ in clothing?

Answers

Answer:

Well it would be 4 percent

Step-by-step explanation:

Thinm of it this way, if you mutliply 25 times 4 it equals 100 then mulitply then 1 dollar by 4 getting 4 dollars worth of tax making it 4 percent of the total ckst

what is the equation of the major axis of y=1/x

Answers

The equation of the major axis of y = 1 / x would be y = x and y = -x.

How to find the equation ?

The equation y = 1/x constitutes a rectangular hyperbola. Not like ellipses possessing broadly characterized principal axes, no finite line exists representing the major axis of the given hyperbola.

This is due to the symmetrical relationship around both x- and y-axes where its core remains positioned at (0, 0). In place of a definite line, the asymptotes operate in replaceable fashion, defined as the lines y = x and y = -x, which are values approached at near limit by this specific hyperbola yet never collided with.

Find out more on major axis at https://brainly.com/question/30950392

#SPJ1

find the slope of this graph

find the slope of this graph

Answers

Answer:

-3

Step-by-step explanation:

If I have $100 dollars and spend $99.99 dollars, how much money do I have left?

Answers

Answer:

You have $00.01

Step-by-step explanation:

100-99.99=0.01

Answer:

A cent.

Step-by-step explanation:

100 - 99.99 = 0.01

You would have $0.01, or a cent, left.

Hope this helps.

Karl spent $30 decorating for the annual holiday party. Each, x, table cover cost $2
and each, y, center piece cost $6. Karl bought 7 items total.

what are the first and second equation?

Answers

The two pair of linear equations are 2x+6y=30 and x+y=7.

What is a linear system of equations?

A system of linear equations consists of two or more equations made up of two or more variables such that all equations in the system are considered simultaneously. The solution to a system of linear equations in two variables is any ordered pair that satisfies each equation independently.

Each, x, table cover cost $2 and each, y, center piece cost $6.

Karl spent $30 decorating for the annual holiday party.

So, the equation is 2x+6y=30 --------(I)

Karl bought 7 items total.

Now, x+y=7 --------(II)

From equation (II), x=7-y

Substitute, x=7-y in equation (I), we get

2(7-y)+6y=30

14-2y+6y=30

14+4y=30

4y=16

y=4

Substitute y=4 in equation (II), we get

x=3

Therefore, the two pair of linear equations are 2x+6y=30 and x+y=7.

To learn more about the linear system of an equations visit:

https://brainly.com/question/27664510.

#SPJ1

a store is having a 20% off sale on all merchandise. if mai buys one item and saves $13, what was the original price of her purchase

Answers

I think it’s 65. (Please correct me if I’m wrong!)

Will mark Brianliest please answer :)

Will mark Brianliest please answer :)

Answers

Answer:

3.5×10^4=35000

Step-by-step explanation:

Consider the value

3.5

we are saying that we are counting in units (1's) in that we have

3

1

2

of 1's

'.....................................................................................

Consider the value

3.5

×

10

. Now we are saying we have

3

1

2

of tens. That is; 3 lots of 10 is 30 and

1

2

of 10 is 5 so we have

30

+

5

=

35

'.................................................................................

Note that

10

2

is 100

Consider the value

3.5

×

10

2

. Now we are saying we have

3

1

2

of

100

'

s

So if we are counting in 100's then the decimal point stays where

it is and we move the number of 3.5 to the left until the

3 becomes hundreds.

Note that we have to insert a place holder of 0 just to the left of the decimal point to make sure the three is viewed as in the hundreds.

3.5

×

10

2

−−−−−−−−−−−−−−−−−−→

slide to the left 2 places

350.0

1. Wesam buys an iPod for $120 and gets consumer surplus of $80.

a. What is her willingness to pay?

b. If she had bought the iPod on sale for $90, what would her consumer

surplus have been?

c. If the price of an iPod were $250, what would her consumer surplus

have been?

Answers

Consumer surplus is a valuable tool for measuring the satisfaction that consumers derive from a product. It helps to understand how much value consumers place on a product and how much they are willing to pay for it.

Consumer surplus is a measure of the difference between the maximum amount that a consumer is willing to pay for a product and the actual price paid. In this scenario, Wesam buys an iPod for $120 and gets a consumer surplus of $80. Therefore, her willingness to pay for the iPod would be $200 ($120 + $80).
If Wesam had bought the iPod on sale for $90, her consumer surplus would have been $110 ($200 - $90). This is because she would have paid less for the product, but her willingness to pay would remain the same at $200.
If the price of an iPod were $250, Wesam's consumer surplus would be zero. This is because her willingness to pay for the iPod is $200, and if the price of the iPod is higher than that, she would not purchase the product. Therefore, she would have no consumer surplus.
In summary, consumer surplus is a valuable tool for measuring the satisfaction that consumers derive from a product. It helps to understand how much value consumers place on a product and how much they are willing to pay for it.

To know more about Consumer visit:

https://brainly.com/question/28537213

#SPJ11

given eigenvalues, eigenvectors for matrix A are λ1 = 2, v1 = [-5 1]t and λ2 = 6, v2 = [5 4]t
(t means transpose ... means the row vector is actually a column vector)
Defn of Eigenvector, Eigenvalue:
Avi = λivi for all i, in this case, i = 1, 2

Answers

The eigenvectors v1 and v2 are such that when multiplied by matrix A, they result in scalar multiples of themselves (scaled by their respective eigenvalues).

An eigenvector is a non-zero vector that, when multiplied by a matrix, results in a scalar multiple of itself. In other words, if A is a square matrix and v is an eigenvector of A, then Av = λv, where λ is the eigenvalue associated with v.

Given the eigenvalues and eigenvectors for matrix A as λ1 = 2, v1 = [-5 1]ᵀ and λ2 = 6, v2 = [5 4]ᵀ, we can say that:

- Av1 = λ1v1 = 2[-5 1]ᵀ = [-10 2]ᵀ
- Av2 = λ2v2 = 6[5 4]ᵀ = [30 24]ᵀ

Therefore, the eigenvectors v1 and v2 are such that when multiplied by matrix A, they result in scalar multiples of themselves (scaled by their respective eigenvalues).

learn more about eigenvector

https://brainly.com/question/31013028

#SPJ11

I am politely asking for some assistance with, thy questions in quantities above 1. My very brain inside of my cranium is too little to answer thy questions. I am requesting some assistance.

I am politely asking for some assistance with, thy questions in quantities above 1. My very brain inside
I am politely asking for some assistance with, thy questions in quantities above 1. My very brain inside
I am politely asking for some assistance with, thy questions in quantities above 1. My very brain inside

Answers

Answer:

First one, true

Second one, 23/45

Third one, 11/29

Step-by-step explanation:

There's thy answer for thy self t-t

Answer:

1.)true

2.) 23/45

3.)11/29

Step-by-step explanation:

-3x (- -8x+52+:
+5+3)
A. 11x²8x-9
11x³8x² - 9x
B.
C. 24x³15x² - 9x
D.
24x²15x - 9

Answers

Answer:

To simplify the expression -3x(-8x+52+5+3), we can distribute the -3x to each term inside the parentheses:

-3x(-8x+52+5+3) = 24x² - 156x - 15x - 9x

Simplifying further by combining like terms, we get:

-3x(-8x+52+5+3) = 24x² - 180x - 9x

Therefore, the simplified expression is 24x² - 189x. None of the options given match this answer. Therefore, there seems to be an error in the original question.

Step-by-step explanation:

Other Questions
What is the first intervention for a client experiencing myocardial infarction? A) Administer morphineB) Administer oxygenC) Administer sublingual nitroglycerineD) Obtain an electrocardiogram quick! i need help, what is the ceo of vouge ney york times best seller?!?! PLEASE HELP! WILL MEDAL! 1. Write the balanced equation for the reaction between zinc and acetic acid? 2. Classify the reaction between zinc and acetic acid and explain, in general terms, what happens during this type of reaction? 3. Give an example of a type of element and a type of compound that are likely to participate in this type of reaction? The cooking time for a cake is 25 minutes correct to the nearest 5 mins. What is the longest cooking time for the cake (2 d.p.)? Need helpFor childhood education class:-How do you make structure and activity for 1st grade math class? Why was the discovery of gold in the Klondike so exciting? ok so im thinking a number between 1 and 10 whoever get's it right gets a brainliest.because yall need somthing to cheer yall up (Middle school math) please help, thank you! A worker bee has a mass of 1 x 10 ^-4 kg there are 4 x 10 ^4 bees living in one hive together what is the mass of all the worker bees in the hive together? (scientific notation) The earth-atmosphere thermal equilibrium temperature is maintained because: Group of answer choices of the movement of latent heat from north to south across the equator. global warming is driving the earth-atmosphere system closer to a pure blackbody. the polar ice caps are melting in order to maintain ocean temperatures. none of the other answers. energy radiated equals energy absorbed. which region in Africa is the poorest When plotting points on the coordinate plane below, which point would lie on the y-axis?? Definition of home1.2. I RESLLY NEED THIS NOW The simple interest owed on a loan of $5,600 after 4 years is $1,008. What percentrepresents the annual interest rate on the loan? Record your answer on the grid. You have $5,700 at a local bank. You hear a rumor that the bank is going to fail. You rush over to the bank to withdraw your money and find many other bank customers who all want to withdraw their money from the bank. The scenario described here is a:Group of answer choicesregular day at the bank.bank run.sale of government bonds.result of the Federal Reserve being the lender of last resort. How many carbon atoms are represented by the model below?A. 2OB. 3C. 1O D.O The specific heat of a substance is a measure of how much energy is required to raisethe ______one degree per one unit of mass. There are 10 girls and 16 boys in a class. The teacher has sticks with each students name on them in a bag. What is the probability of selecting sticks with a boys name and then a girls name if the first stick is not replaced? A: 40/169.B: 16/65.C: 45/128.D: 26/51. europeans establish social hierarchies in the New World that were defined primarily by how do you know if a pair of values (x,y) is a solution to an equation?