If $\tan \alpha = \frac{1}{7},\;\tan \beta = \frac{1}{3},$ then $\cos 2\alpha = $
If $\tan \alpha = \frac{1}{7},\;\tan \beta = \frac{1}{3},$ then $\cos 2\alpha = $
- A
$\sin 2\beta $
- B
$\sin 4\beta $
- C
$\sin 3\beta $
- D
None of these
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