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      <text>4.3.3.2 Double angle formula</text>
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      <text><![CDATA[<h4>Double angle formulae</h4>
<p>If we put \(B=A\) in the identity \(\sin (A+B)\equiv\sin A\cos B+\cos A\sin B\) we obtain<br></p>

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<h4>Key Point</h4>
\[\sin 2A\equiv\sin A\cos A+\cos A\sin A\]
<p>so</p>
\[\sin 2A\equiv 2\sin A\cos A\]
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