Question

If 8x + 8y = 18 and x^2 – y^2 = –3/8, what is the value of 2x – 2y?

The answer is supposed to be -1/3 but I have no idea how to get that. Thanks in advance for helping out!

Answer 1

from 8x + 8y = 18
x + y = 9/4

x^2 - y^2 = (x+y)(x-y) , using the difference of squares
-3/8 = (9/4)(x-y)
x-y = (-3/8) / (9/4) = (-3/8)(4/9) = -1/6
so 2x - 2y = .......

Answer 2

This was incredibly helpful, thanks!