The difference between the absolute maximum and absolute minimum values of the function $f(x)=2 x^3-15 x^2+36 x-30$ on $[-1,4]$ is

If $f(x)=x e^{x(1-x)}, x \in R$, then $f(x)$ is

The angle between the curves $y^2=x$ and $x^2=y$ at the point $(1,1)$ is

If the tangent of the curve $x y+a x+b y=0$ at $(1,1)$ makes an angle $\tan ^{-1} 2$ with $X$-axis, then $\frac{a b}{a+b}=$