If a + 1/a = 5 then a3 + (1/a3) is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is Option 2 i.e. 110.
| Understanding/Application |
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(a + b)3 = a3 + b3 + 3ab(a + b) a3 + b3 = (a + b)3 - 3ab(a + b) |
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a + 1/a = 5 a3 + 1/a3 = (a + 1/a)3 - 3a(a + b)/a = (a + 1/a)3 - 3(a + b) = 53 - 3(5) = 125 - 15 = 110 |