please help with substitution!?

Question

x-2y=8
y=-4x+5

and

x-2y=0
3x+y=0

Answer 1

1. problem: x - 2y = 8
given : y = -4x + 5

let x = unknown

to solve:
x - 2(-4x + 5) = 8
x + 8x - 10) = 8
9x - 10 = 8
9x = 8 + 10
9x = 18
x = 18/9
x = 2

to solve for y: since y = -4x + 5
and x = 2,
then y = -4(2) + 5
y = -8 + 5
y = -3

To prove, go back to the problem x - 2y = 8.
Convert x & y based on the amounts arrived at.
Since x = 2
and y = -3
then: x -2y = 8
2 -2(-3) = 8
2 + 6 = 8

2. answer must be 0 for both x & y

Answer 2

x - 2y = 8

y = - 4x + 5

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x - 2y = 8

x - 2(- 4x + 5) = 8

x + 8x - 10 = 8

The distributive property on the right side of the equation

9x - 10 + 10 = 8 + 10

Adding + 10 to both sides of the equation

9x = 18

9x/9 = 18/9

Dividing both sides of the equation by 9

x = 2

The solution set is { 2 }

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Solving for y

y = - 4x + 5

y = - 4(2) + 5

y = - 8 + 5

y = - 3

The solution set is { - 3}

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Check

x - 2y = 8

2 -(-3) = 8

2 + 6 = 8

8 = 8

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y = - 4x + 5

-3 = - 4(2) + 5

-3 = - 8 + 5

- 3 = - 3

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The answer is

x = 2

y = - 3

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The second probem

x = 0

y = 0

Answer 3

Okay, for the first one: you know that y=-4x+5. So you substitute that in for y in the first equation. You'll get x-2(-4x+5)=8. Distribute the -2, you get x+8x-10=8. Keep working it out, add x to 8x to get 9x, and add 10 to 8 to get 18. It looks like 9x=18. Then divide 18 by 9 to get 2. x=2. Then put that value into the second equation to get y=-4(2)+5. Work it out to get y=-8+5. And, finally, y=-3. x=2, y=-3
For the second one, you need to get one variable by itself on one side of the equal sign. I'll do it w/ the first one. Take x-2y=0 and add 2y to both sides to get x=2y. Substitute that value into the second equation to get 3(2y)+y=0. Work it out to 6y+y=0, then 7y=0. Divide 0 by 7 to get 0. y=0. Then put that value back into the first equation. x-2(0)=0. Work it out to get x-0=0, and, finally, x=0. In this problem, both x and y equal 0.
GL

Answer 4

you do not need given variable values
you have
x-2y=8
y=-4x+5

Use the first one and solve for x
x-2y=8
add 2y to both sides
x=8+2y
now substitute this equation of x into the second equation
y=-4(8+2y)+5
simplify
y=-32-8y+5
simplify
y=-27-8y
add 8y to both sides
9y= -27
divide both sides by 9
y= -3
now substitute this value of y into the equation that we found x to be earlier
x=8+2(-3)
simplify
x=2
so therefore
x=2 and y= -3


Now do the same thing for the second set of equations.

Answer 5

So in the first you should have one equation of x - 2(-4x+5) = 8 Distribute then solve.

The second one you will have to solve for either x or y first, then try substitution.

Answer 6

The first one X= 2 and y = --3
The second X and Y = 0

Answer 7

for the first x=2 y=-3
for the second i get x and y =0

Answer 8

u cant solve those like that. u need variables, numbers to replace the x and y.
(ex: x=2, y=4 )

Answer 9

oh come on....... solve for one of the variables x or y, then substitute that value back into the equation to get the other one.

weren't you listening in school today?????

Answer 10

1st set x=2, y=-3

2nd set x=0, y=0


i do by elimination method which is easier