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PART - 1 CH - 3 Trigonometric Functions — Maths STD 11 Science — Question

CBSE BoardEnglish MediumSTD 11 ScienceMathsPART - 1 CH - 3 Trigonometric Functions1 Mark
Question
Find the value of expression $\left\{\cos A \cdot \cos \left(90^{\circ}- A \right)\right\}$.
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Answer


$\begin{aligned} \text {Given expression } & =\cos A \cdot \cos \left(90^{\circ}- A \right) \\ & =\cos A \cdot \sin A \\ & =\sin A \cdot \cos A =\frac{1}{2} \times 2 \sin A \cdot \cos A \\ & =\frac{1}{2} \sin 2 A\end{aligned}$

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