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How do I evaluate $\sin \left(\sec^{-1}\left(\frac{-7}{5}\right)\right)$?

The answer given is $\frac{2\sqrt{6}}{7}$, but I have no idea how to get it. Hope someone can explain it for me. Thanks in advance.

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\begin{align} \sin \left(\sec^{-1} \left( -\frac75\right)\right) &= \sin \left(\cos^{-1} \left( -\frac57\right)\right)\\ &=\frac{\sqrt{7^2-5^2}}{7} \end{align}

where the last line is due to Pythagoras Theorem. Also think of which quadrant is $\cos^{-1}\left( -\frac57 \right)$ located.

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