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If 5(tan^2x - cos^2x)=2cos 2x + 9, then ...

If `5(tan^2x - cos^2x)=2cos 2x + 9`, then the value of cos4x is

A

`-7/9`

B

`-3/5`

C

`1/3`

D

`2/9`

Text Solution

AI Generated Solution

To solve the equation \( 5(\tan^2 x - \cos^2 x) = 2 \cos 2x + 9 \) and find the value of \( \cos 4x \), we can follow these steps: ### Step 1: Rewrite \( \tan^2 x \) We know that \( \tan^2 x = \sec^2 x - 1 \). Therefore, we can rewrite the equation as: \[ 5(\sec^2 x - 1 - \cos^2 x) = 2 \cos 2x + 9 \] ...
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