3.Trigonometrical Ratios, Functions and Identities
medium

यदि $\tan \alpha = \frac{1}{7},\;\tan \beta = \frac{1}{3},$ तब  $\cos 2\alpha = $

A

$\sin 2\beta $

B

$\sin 4\beta $

C

$\sin 3\beta $

D

इनमें से कोई नहीं

Solution

(b) $\cos 2\alpha = \frac{{1 – {t^2}}}{{1 + {t^2}}} = \frac{{24}}{{25}}$    {यहाँ  $t = \tan \alpha $}

$\sin 2\beta = \frac{{2T}}{{1 + {T^2}}} = \frac{3}{5} \Rightarrow \cos 2\beta = \frac{4}{5}$   {$T = \tan \beta $}

$\therefore \,\,\sin 4\beta = 2\sin 2\beta \cos 2\beta $

$= 2.\frac{3}{5}.\frac{4}{5} = \frac{{24}}{{25}} = \cos 2\alpha $.

Standard 11
Mathematics

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