Question

Use substitution to solve the system
5x + 8y= −25
4x − 5y= −20

(x,y)= ( , )

Answer 1

we can also use substitution. :P

Answer 2

Hero beat me to it... touche

Answer 3

by the looks of it, waaay before i did.. good job

Answer 4

1. Solve for y:

y = (-25 - 5x)/8
y = (20 + 4x)/5

2. Substitute y = y:

(-25 - 5x)/8 = (20 + 4x)/5

3. Cross Multiply:
5(-25 - 5x) = 8(20+4x)

4. Continue Solving for x:

-125 - 25x = 160 + 32x

57x = -285

x = -285/57 = -5
y = 0

Answer 5

Robtobey always tries to come in behind me. I made a mistake, but corrected it

Answer 6

Did you post something?

Answer 7

me? i was about to, im just looking it over trying it myself,but be prepared if i end up asking u a question later bout it

Answer 8

Okay. It's not the traditional version of substitution, but it's still substitution. It can be seen as substitution or elimination really because you're substituting the equation of y in terms of x and eliminating the y variable at the same time.

Answer 9

So in a way, it's the combo version

Answer 10

yeah it did look different than what im use to

Answer 11

It's just solving for y and setting it equal to each other. The reason I do it that way is sometimes when you use traditional elimination or substitution methods, you can run into a trap that give you false answers. Using my method, you don't run into such traps and you can easily see if there is a solution or if there is no solution.

Answer 12

will it work for most problems like that?

Answer 13

It will work for all of them with no problem. The only thing is....

If you solve for y and the denominators are the same, when you cross multiply, be sure to properly cancel, otherwise you will get a wrong answer