(2)对于三个以上函数的积、商的导数,依次转化为"两个"函数的积、商的导数计算.
[活学活用]
求下列函数的导数:
(1)y=sin x-2x2;(2)y=cos x·ln x;(3)y=.
解:(1)y′=(sin x-2x2)′=(sin x)′-(2x2)′=cos x-4x.
(2)y′=(cos x·ln x)′=(cos x)′·ln x+cos x·(ln x)′
=-sin x·ln x+.
(3)y′=′=
==
复合函数的导数运算
[典例] 求下列函数的导数:
(1)y=;
(2)y=sin2;
(3)y=5log2(2x+1).
[解] (1)设y=u-,u=1-2x2,
则y′=(u-)′(1-2x2)′=·(-4x)
=-(1-2x2)- (-4x)=2x(1-2x2)-.
(2)设y=u2,u=sin v,v=2x+,
则yx′=yu′·uv′·vx′=2u·cos v·2
=4sin vcos v=2sin 2v=2sin.
(3)设y=5log2u,u=2x+1,
则y′=5(log2u)′·(2x+1)′
==.