Question

if x-y =4 and xy =21, find the value of x^3+y^3.

Answer 1

given, x-y = 4 and x-y = 21

(x-y)² = (x+y)² - 4xy

4² = (x+y)² - 4(21)

(x+y)² = 84+16 = 100

x+y = 10

x³+y³ = (x+y)³-3xy(x+y)

x³+y³ = 1000 - 630 = 370