Answer:
316 or -316.
Step-by-step explanation:
x^3 - y^3 = (x - y)(x^2 + xy + y^2)
= 4(x^2 + y^2 + 21)
x - y = 4
xy = 21
Substitute x = 4 + y in the last equation
(4 + y) y = 21
y^2 + 4y - 21 = 0
(y + 7)(y - 3) = 0
y = 3, -7.
So, x = 7, - 3.
So, x and y are 7 and 3 or -7 and -3.
But x^2 + y^2 = 9 + 49 = 58 whichever is true,
So, x^3 - y^3
= 4(x^2 + y^2 + 21)
= 4 (58 + 21)
= 316,
If x = -3 and y = -7 , then the answer is
-316.
