since, $\sin 90$ $=\sin \pi / 2=1$

using the above we get,,

$\sin ^{-1} \frac{1}{5}+\cos ^{-1} x=\frac{\pi}{2}$

$\cos ^{-1} x=\frac{\pi}{2}-\sin ^{-1} \frac{1}{5}$ Using identity: $\sin ^{-1} t+\cos ^{-1} t=\pi / 2$

as, $\cos ^{-1} x=\cos ^{-1} \frac{1}{5}$

Which means that the value of $\mathrm{x}$ is $1 / 5$.