Substitution: 7x+8y=-5, -8x+y=26

Elimination: 4x+5y=1, -8x+10y=2

Ok, we can't do your homework for you, but we can remind you of methods to use or answer questions related to your work.
Have you done this kind of exercise before?

Substitution: 7x+8y=-5, -8x+y=26

We have two equations here. You need to solve them by isolating one of the terms (y or x), then substituting your answer for that term in the equations.

Your best bet would be to pick the second equation and solve for y in terms of x. Then, when you have an equivalent for y in terms of x, substitute that equivalent for all occurrences of y in the first equation. That will give you the value of x. Then take the second equation again and substitute x with the value you just got. Now you have the values of y and x.
Make sense?

I'll give examples. It's really simple:

3x+4 = y
5x+2 = 2y

You agree that y = 3x+4 ? Well the same y is equal to 3x+4 in the second equation, so,

5x+2 = 2(3x+4)

Did you see what I've done? I've replaced 'y' by its corresponding value, that is '3x+4'. Now that there is only one variable, you can work out for 'x' Having found the value of x, now you can find the value of y by replacing x in either equations.

Note that you could also replace x by its corresponding expression in terms of y. However, that you'd be more complicated here since you'll have : 3x+4 = y turned into (y-4)/3, which brings in fractions.

By elimination, you are putting both equations one under the other so that a variable cancels out.

3x+4 = y
5x+2 = 2y

I'll multiply the whole first equation to have:

6x + 8 = 2y
5x + 2 = 2y

Do you see why I multiplied by 2? Now you have 2y on both sides, and one under the other. By subtracting the equations, you'll have:


6x + 8 = 2y
5x + 2 = 2y -
_________
x + 6 = 0

Now you can solve for x here.

Hope it helped! :)

Thanks for the rating YoungHyperLink! :)

Yes, it's often like that. People come and go without looking at their answers, or look at the provided answers and never reply.