If `tanA=1/7a n dtanB=1/3` , show that `cos2A=sin4Bdot`

Explanation

To prove that \( \cos 2A = \sin 4B \) given \( \tan A = \frac{1}{7} \) and \( \tan B = \frac{1}{3} \), we will calculate both \( \cos 2A \) and \( \sin 4B \) step by step.

### Step 1: Calculate \( \cos 2A \)

Using the double angle formula for cosine:
\[ \cos 2A = \frac{1 - \tan^2 A}{1 + \tan^2 A} \]
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