If a3 + b3 = 35 and ab = 6, then what is the value of a + b?
5
8
2
-8
A.
5
Let a + b = x
C.B.S.
(a + b)3 = a3 + b3 + 3ab(a + b)
⟹ x3 = 35 + 3 x 6 x (x)
⟹ x3 - 18x = 35
⟹ x(x2 - 18) = 5 x 7
check with the option,
Now,
⟹ x = 5, x2 -18 = 7
∴ a + b = 5