求y=（1-2x）的10次方的导数?

y=(1-2x)^10
y'=10(1-2x)^9*(-2)
y'=-20(1-2x)^9请问为什么还要乘以（-2）请写出具体详细步骤谢谢。f(u(x)导数，是复合函数：y=f(u(x))dy/dx=df(u(x))/du*du(x)/dx如f(x^2)=df(x^2)/d(x^2)*dx^2/dx=df(x^2)/d(x^2)*2x