815. Find the differentials of the functions:
1) $y=x^{3}$ at the point $x=0$, if $\left.\Delta x=0.3 ; 2\right) y=x^{3}-x^{2}+$ $+3 x-1$; 3) $r=\varphi^{4}+2^{\sin 3 \varphi}$; 4) $y=\ln \left(x^{2}+1\right)+\operatorname{arctg} \sqrt{x}$ at the point $x=1$, if $\Delta x=0.1$.