Tìm đạo hàm của các hàm số sau 

$$\begin{gathered} a, y={\left(x^7-5x^2\right)}^3 ; b, y=\left(x^2+1\right)\left(5+3x^2\right); \\ c, y=\frac{2x}{x^2-1} ; d, y=\frac{3-5x}{x^2-x-1} ; e, y={\left(m+\frac{n}{x^2}\right)}^3 (m,n là các hằng số ) \\ Giải \\ a, y\text{'}=3{\left(x^7-5x^2\right)}^2.\left(x^7-5x^2\right)=3{\left(x^7-5x^2\right)}^2\left(7x^6-10x\right) \\ b, y\text{'}={\left(x^2+1\right)}^{\text{'}}\left(5-3x^3\right)+\left(x^2+1\right).{\left(5-3x^2\right)}^{\text{'}} \\ =2x\left(5-3x^2\right)+\left(x^2+1\right)\left(-6x\right)=-12x^3+4x \\ c, y\text{'}=\frac{2\left(x^2-1\right)-2x2x}{{\left(x^2-1\right)}^2}=\frac{-2x^2-2}{{\left(x^2-1\right)}^2} \\ d ,y\text{'}=\frac{-5\left(x^2-x+1\right)-\left(3-5x\right).\left(2x-1\right)}{{\left(x^2-x+1\right)}^2}=\frac{5x^2-6x-2}{{\left(x^2-x+1\right)}^2} \\ e, y\text{'}=3{\left(m+\frac{n}{x^2}\right)}^2.{\left(m+\frac{n}{x^2}\right)}^{\text{'}}=-\frac{6n}{x^3}{\left(m+\frac{n}{x^2}\right)}^2 \end{gathered}$$