For the equation $\cos^{-1} x + \cos^{-1} 2x + \pi = 0$,the number of real solutions is:

For $\alpha, \beta, \gamma \neq 0$. If $\sin ^{-1} \alpha+\sin ^{-1} \beta+\sin ^{-1} \gamma=\pi$ and $(\alpha+\beta+\gamma)(\alpha-\gamma+\beta)=3 \alpha \beta$,then $\gamma$ is equal to

$\cot^{-1}(1) + \cot^{-1} (\frac{1}{2}) + \cot^{-1}(\frac{1}{3}) =$

If $y = \tan^{-1} \left( \frac{\ln(e/x^2)}{\ln(ex^2)} \right) + \tan^{-1} \left( \frac{3 + 2 \ln x}{1 - 6 \ln x} \right)$,then $\frac{d^2y}{dx^2} =$

If $x, y, z$ are in $A.P.$ and $\tan^{-1} x, \tan^{-1} y, \tan^{-1} z$ are also in another $A.P.$,then:

If $\sin ^{-1} x + \sin ^{-1}(1-x) = \cos ^{-1} x$,then $x \in$