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The value of \(\sin\left(2\sin^{-1}\frac{3}{5}\right)\) is equal to

  • A.\(\frac{23}{25}\)
  • B.\(\frac{21}{25}\)
  • C.\(\frac{22}{25}\)
  • D.\(\frac{24}{25}\)
  • E.\(\frac{18}{25}\)

Answer: D

The value is \(\frac{24}{25}\).

Let \(\theta = \sin^{-1}\frac{3}{5}\), so \(\sin\theta = \frac{3}{5}\) and, since \(\theta\) is acute, \(\cos\theta = \frac{4}{5}\).

\[ \begin{aligned} \sin 2\theta &= 2\sin\theta\cos\theta \\ &= 2 \cdot \tfrac{3}{5} \cdot \tfrac{4}{5} = \tfrac{24}{25} \end{aligned} \]

\(\frac{18}{25}\) comes from using \(2\sin^{2}\theta\), and \(\frac{7}{25}\) (not offered) would be \(\cos 2\theta\). The remaining options do not arise from a standard formula.

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