Question:
The value of $\sin \left(2 \sin ^{-1}(.6)\right)$ is
(a) 0.48
(b) 0.96
(c) 1.2
(d) sin 1.2
Solution:
$\sin \left(2 \sin ^{-1} 0.6\right)$
$=\sin \left[\sin ^{-1}\left(2 \times 0.6 \times \sqrt{1-(0.6)^{2}}\right)\right]$ $\left[2 \sin ^{-1} x=\sin ^{-1}\left(2 x \sqrt{1-x^{2}}\right)\right]$
$=\sin \left[\sin ^{-1}(2 \times 0.6 \times \sqrt{1-0.36})\right]$
$=\sin \left[\sin ^{-1}(2 \times 0.6 \times \sqrt{0.64})\right]$
$=\sin \left[\sin ^{-1}(2 \times 0.6 \times 0.8)\right]$
$=\sin \left[\sin ^{-1}(0.96)\right]$
$=0.96$ $\left[\sin \left(\sin ^{-1} x\right)=x, \forall x \in[-1,1]\right]$
Hence, the correct answer is option (b).