Question

If a − b = 2, ab = 15, find a³ − b³.

Answer 1

Here, a − b = 2, ab = 15,

Using the identity:

a³ − b³ = (a − b)³ + 3ab (a − b)

a³ − b³ = (2)³ + 3(15) (2)

a³ − b³ = 8 + 3(30)

a³ − b³ = 8 + 90

∴ a³ − b³ = 98