Question

If a + b = 4 and ab = 3, then what is the value of a3 + b3?

A) 21 B) 17 C) 28 D) 31

Answer 1

Since we know that (a + b)3 = a3 + b3 + 3ab(a + b),

put all the values given

⇒ 4^3 = a3 + b3 + 3 × 3(4)

64=a3 + b3+3×12

64= a3 + b3+36

a3 + b3=64-36

⇒ a3 + b3 = 28

I hope this helps you.

∴ the value of a3 + b3 is 28