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Question
Differentiate sin2 (2x + 1) ?
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Solution
\[\text{ Let } y = \sin^2 \left( 2x + 1 \right)\]
\[\text{Differentiate it with respect to x we get }, \]
\[\frac{d y}{d x} = \frac{d}{dx}\left[ \sin^2 \left( 2x + 1 \right) \right]\]
\[ = 2\sin\left( 2x + 1 \right)\frac{d}{dx}\sin\left( 2x + 1 \right) \left[ \text{ using chain rule } \right]\]
\[ = 2\sin\left( 2x + 1 \right) \cos\left( 2x + 1 \right) \frac{d}{dx}\left( 2x + 1 \right) \left[ \text{ using chain rule } \right] \]
\[ = 4\sin\left( 2x + 1 \right) \cos\left( 2x + 1 \right)\]
\[ = 2\sin2\left( 2x + 1 \right) \left[ \because \sin2A = 2\sin A\cos A \right]\]
\[ = 2 \sin\left( 4x + 2 \right)\]
\[So, \frac{d}{dx}\left\{ \sin^2 \left( 2x + 1 \right) \right\} = 2 \sin\left( 4x + 2 \right)\]
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