1.

If a3 + b3 = 62 and a + b = 2, then the value of ab is:1. -62. 93. 64. -9

Answer» Correct Answer - Option 4 : -9

Given:

a + b = 2

a3 + b3 = 62

Formula used:

(a + b)3 = a3 + b3 + 3ab(a + b)

Calculation:

a + b = 2

Cubing the given equation

(a + b)3 = 23

⇒ a3 + b3 + 3ab(a + b) = 8      ----[(a + b)3 = a3 + b3 + 3ab(a + b)]

⇒ 62 + 3ab × 2 = 8      ----(a3 + b3 = 62, a + b = 2)

⇒ 6ab = 8 – 62

⇒ 6ab = -54

⇒ ab = -54/6 = -9

∴ The value of ab is -9.



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