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3.Trigonometrical Ratios, Functions and Identities
easy
$\frac{{\sin 3A - \cos \left( {\frac{\pi }{2} - A} \right)}}{{\cos A + \cos (\pi + 3A)}} = $
A
$\tan A$
B
$\cot A$
C
$\tan 2A$
D
$\cot 2A$
Solution
(d) $\frac{{\sin 3A – \cos \left( {\frac{\pi }{2} – A} \right)}}{{\cos A + \cos (\pi + 3A)}}$
$ = \frac{{\sin 3A – \sin A}}{{\cos A – \cos 3A}}$
$=\frac{{2\cos 2A\sin A}}{{2\sin 2A\sin A}}$
$= \frac{{\cos 2A}}{{\sin 2A}} = \cot 2A$.
Standard 11
Mathematics
