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