Trigonometric Identities Question 128

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

[CET 1989]

Options:

A) $ \sin B $

B) $ \sin 2B $

C) $ \sin 3B $

D) None of these

Show Answer

Answer:

Correct Answer: B

Solution:

$ A+B=45{}^\circ , $ therefore $ 2A=90{}^\circ -2B $
$ \therefore \cos 2A=\sin 2B $ .