If $y=t^2+t^3$ and $x=t-t^4$, then $\frac{d^2 y}{d x^2}$ at $t=1$ is

If $y=\tan (\log x)$, then $\frac{d^2 y}{d x^2}=$

For $x<0, \frac{d}{d x}\left[|x|^x\right]=$

If $y=x-x^2$, then the rate of change of $y^2$ with respect to $x^2$ at $x=2$ is