It is known that x + y = 4, x2-y2 = 20, then the value of X-Y is______ ．

It is known that x + y = 4, x2-y2 = 20, then the value of X-Y is______ ．

∵ x2-y2 = 20, ∵ x + y (X-Y) = 20, and ∵ x + y = 4, ∵ X-Y = 20 △ 4 = 5

8y = 5x, then x and Y () x * 8 = y * 3, then x; y = (); () when x = 1.2, y = ()

If 8y = 5x, then x and y are proportional
X * 8 = y * 3, then x; y = (3): (8)
When x = 1.2, y = (3.2)

X + y = 127 0.5x + 0.8y = 83 sum X and Y
But there's only one best answer,

x+y=127
0.5x+0.8y=83 x+1.6y=166
Subtract the above from the following equation:
0.6y=39
y=65,x=62

Given: x + y + Z = 0,5x-3y-z = 0, find the value of: 5x-y + Z / 2x + 8y + 7z

x+y+z=0,.(1)
5x-3y-z=0.(2)
(1) + (2)
6x-2y=0
2y=6x
y=3x
Substituting (1), we get
x+3x+z=0
z=-4x
therefore
5x-y+z/2x+8y+7z
=(5x-3x-4x)/(2x+24x-28x)
=(-2x)/(-2x)
=1