Question:
Find the real solution of the equation
$\tan ^{-1} \sqrt{x(x+1)}+\sin ^{-1} \sqrt{x^{2}+x+1}=\frac{\pi}{2}$
Solution:
Given equation,
$\tan ^{-1} \sqrt{x(x+1)}+\sin ^{-1} \sqrt{x^{2}+x+1}=\frac{\pi}{2}$
$\tan ^{-1} \sqrt{x(x+1)}=\frac{\pi}{2}-\sin ^{-1} \sqrt{x^{2}+x+1}$
$=\cos ^{-1} \sqrt{x^{2}+x+1}$
$=\tan ^{-1} \frac{\sqrt{-x^{2}-x}}{\sqrt{x^{2}+x+1}}$ (From figure)
$\sqrt{x(x+1)}=\frac{\sqrt{-x^{2}-x}}{\sqrt{x^{2}+x+1}}$
$x^{2}+x=0$
$x=0,-1$
Hence, the real solutions of the given trigonometric equation are 0 and -1.
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