Question

Given the equation below what is the value of y-x?
3x+4=-5y+8
9x+11y=-8

Answer 1

`-5`

Explanation:

`3x+4=-5y+8\\9x+11y=-8`

Rearrange the first equation and substitute it into the second equation.

`3x=-5y+8-4\\3x=-5y-4`

(as we want 9x instead of 3x we are going to multiply this equation by 3)

`9x=-15y-12\\-15y-12+11y=-8\\-4y=4\\y=-1`

Rearrange the first equation and substitute in our y value to solve for x.

`3x+4=-5(-1)+8\\3x=5+8-4\\3x=9\\x=3`

Hence

`y-x=-1-4=-5`