Double-angle values from a given ratio

Double-angle values from a given ratio

Secondary 4

TGM Original Questions

Given that \(\cos A=-\dfrac{8}{17}\) and \(90^\circ<A<180^\circ\), find the exact values of \(\sin 2A\) and \(\cos 2A\).

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Answer:\(\sin 2A=-\dfrac{240}{289}\), \(\cos 2A=-\dfrac{161}{289}\).

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