Question

If x + 5y = 10; find the value of x³ + 125y³ + 150xy − 1000.

Answer 1

Given

⇒ x + 5y = 10

Cubing both sides we get:

⇒ (x + 5y)³ = 10³

⇒ x³ + (5y)³ + 3 × x × 5y × (x + 5y) = 1000

⇒ x³ + 125y³ + 15xy × 10 = 1000

⇒ x³ + 125y³ + 150xy − 1000 = 0

Hence, x³ + 125y³ + 150xy − 1000 = 0