If a –b = 18 and a3 – b3 = 324, then find ab.
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e -102
| Understanding | Application |
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We know the expansion of (a-b)3 which is ⇒ (a - b)3 = a3 - b3 - 3ab(a - b) ⇒ a3 - b3 = (a-b)3 + 3ab(a-b) |
We know that, a3 – b3 = 324 a –b = 18 By putting the value of them in the given equation, ⇒ a3 - b3 = (a-b)3 + 3ab(a-b) ⇒ 324 = 5832 + 3ab(18) ⇒ 54ab = -5508 ⇒ ab = -102 |