x + 2x + 1 = 5x হলে, \(x + \frac{1}{x}\) = কত ?

A \(\sqrt 3 \) 

B

C

D \(\sqrt 5 \) 

Solution

Correct Answer: Option D

x4+2x2 +1 = 5x2

বা,   x+1 = 3x 

বা, x2  \((x2 + \frac{1}{{x2}}) = 3x2\) বা,  \(x2 + \frac{1}{{x2}} = 3\) বা,  \((x + \frac{1}{x})2 - 2.x.\frac{1}{x} = 3\) বা,  \((x + \frac{1}{x})2\)  = 3+2 

  \(x + \frac{1}{x} = \sqrt 5 \)  

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