Question

if x -y is equals to 4 and x y is equals to 21 find x cube - y cube

Answer 1

Given
x - y = 4
and xy = 21

x - y = 4

=> (x - y)² = (4)²

=> x² + y² - 2xy = 16

=> x² + y² - 2(21) = 16

=> x² + y² - 42 = 16

=> x² + y² = 58


Now x³ - y³ = (x - y)(x² + y² + xy)

=> x³ - y³ = (4)(58 + 21)

=> x³ - y³ = (4)(79)

=> x³ - y³ = 316

Hope it helps dear friend ☺️✌️

Answer 2

Please see the attachment