যদি 4a2 + 1/a2 = 2 হয়, তবে 8a3 + 1/a3 এর মান কত?

B 1

C 2

D 5

Solution

Correct Answer: Option A

দেওয়া আছে ,
4a2 + 1/a2 = 2
⇒ (2a)2 + (1/a)2 = 2
⇒ (2a + 1/a)2 - 2.2a.1/a = 2
⇒ (2a + 1/a)2 = 2 + 4
⇒ (2a + 1/a)2 = 6  ∴ 2a + 1/a =√6

এখন, 
8a3 + 1/a3 = (2a)3 + (1/a)3
= (2a + 1/a)3 - 3.2a.1/a (2a +1/a)
= (√6)3 - 6.√6
= 6√6 - 6√6
= 0

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