Решить дифференциал ..очень надо!!! y(x)= x/5+x ; d2y-?

[latex]y(x)= \frac{x}{5+x} \\\\d^2y=d(dy)\; ,\; \; \; dy=y'(x)\, dx\\\\y'(x)= \frac{1\cdot (5+x)-x\cdot 1}{(5+x)^2} = \frac{5}{(5+x)^2} \\\\dy=\frac{5}{(5+x)^2}\, dx\\\\d^2y=y''dx^2\\\\y''= \frac{-5\cdot 2(5+x)}{(5+x)^4} = \frac{-10}{(5+x)^3}\\\\d^2y=-\frac{10}{(5+x)^2}\, dx^2 [/latex]