MCQ
If $y=\frac{1+\frac{1}{x^2}}{1-\frac{1}{x^2}}$ then $\frac{d y}{d x}$ is equal to
- A$\frac{-4 x}{x^2-1}$
- B$\frac{1-x^2}{4 x}$
- C$\frac{-4 x}{\left(x^2-1\right)^2}$
- D$\frac{4 x}{x^2-1}$
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$\sin ^{-1}\left(\sum_{i=1}^{\infty} x^{i+1}-x \sum_{i=1}^{\infty}\left(\frac{x}{2}\right)^i\right)=\frac{\pi}{2}-\cos ^{-1}\left(\sum_{i=1}^{\infty}\left(-\frac{x}{2}\right)^i-\sum_{i=1}^{\infty}(-x)^i\right)$
lying in the interval $\left(-\frac{1}{2}, \frac{1}{2}\right)$ is. . . . .
(Here, the inverse trigonometric functions $\sin ^{-1} x$ and $\cos ^{-1} x$ assume values in $\left[-\frac{\pi}{2}, \frac{\pi}{2}\right]$ and $[0, \pi]$, respectively.)