Question

The value of $\frac{cos3\theta }{2cos2\theta -1}$ is equal to

• A. $cos\theta$
• B. $sin\theta$
• C. $tan\theta$
• D. none of these

Answer 1

The correct option is C

$tan\theta$

We have,

$\therefore \frac{cos3\theta }{2cos2\theta -1}=\frac{4co{s}^3\theta -3cos\theta }{2(2co{s}^2\theta -1)-1}[\because cos3\theta =4co{s}^3\theta -3cos\theta ]=\frac{4co{s}^2\theta -3cos\theta }{4co{s}^2\theta -2-1}=\frac{4co{s}^2\theta -3cos\theta }{4co{s}^2\theta -3}=cos\theta \left(\frac{4co{s}^2\theta -3}{4co{s}^2\theta -3}\right)=cos\theta$