Question

find the value of x^3+y^3+15xy_125 if x+y=5

Answer 1

cube both the sides n then you'll get the answer.

x+y = 5
(x+y)3 = 125
x3 + y3 + 3x2y + 3xy2 = 125
x3 + y3 + 3xy(x+y) = 125
x3 + y3 + 15xy = 125. [since, x+y = 5]

Hence, found!