a – 1/a = 3 হলে, a4 + 1/a4 = ?  

A    109

B    119

C    129

D    116

Solution

Correct Answer: Option B

 

Sol: (a-1/a)^2 = 3^2 => a^2 -2.a.1/a + 1/a^2 =9 => a^2 + 1/a^2 =11

=>( a^2 + 1/a^2)^2 =(11)^2

=>a^4 +2.a^2.1/a^2 + 1/a^4=121

=>a^4+1/a^4=119

 

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