If tan A = frac{1}{2},tan B = frac{1}{3}, then cos 2A =

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3.Trigonometrical Ratios, Functions and Identities

easy

If $\tan A = \frac{1}{2},\tan B = \frac{1}{3},$ then $\cos 2A = $

A

$\sin B$

B

$\sin 2B$

C

$\sin 3B$

D

None of these

Solution

(b) $A + B = 45^\circ ,$

therefore $2A = 90^\circ – 2B$

$\therefore \cos 2A = \sin 2B$.

Standard 11

Mathematics

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(IIT-1988)