11. The number of real solutions of $\tan - 1 \sqrt { } ( x ( x + 1 ) ) + \sin - 1 \sqrt { } ( x 2 + x + 1 ) = \pi / 2$ is: (A) zero (B) one (C) two (D) infinite
11. The number of real solutions of\\
$\tan - 1 \sqrt { } ( x ( x + 1 ) ) + \sin - 1 \sqrt { } ( x 2 + x + 1 ) = \pi / 2$ is:\\
(A) zero\\
(B) one\\
(C) two\\
(D) infinite\\