১.
$tan\theta =\{1\over 2\}$ হলে $sin2\theta $ এর মান কোনটি?
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$3\over 4$
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$4\over 3$
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$5\over 4$
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$4\over 5$
ব্যাখ্যা
$\begin{aligned} \sin 2 \theta & =\frac{2 \tan \theta}{1+\tan ^2 \theta} \\ & =\frac{2 \cdot \frac{1}{2}}{1+\left(\frac{1}{2}\right)^2}\left[\because \tan \theta=\frac{1}{2}\right] \\ & =\frac{1}{1+\frac{1}{4}}=\frac{1}{5}=1 \times \frac{4}{5}=\frac{4}{5} .\end{aligned}$