(1)设y=u,u=1-2x2,
则y′=(u)′(1-2x2)′=·(-4x)
=(1-2x2) (-4x)= .
(2)设y=eu,u=sin x,
则yx′=yu′·ux′=eu·cos x=esin xcos x.
(3)设y=sin u,u=2x+,
则yx′=yu′·ux′=cos u·2=2cos.
(4)设y=5log2u,u=2x+1,
则y′=5(log2u)u′(2x+1)x′==.
复合函数的求导步骤
求下列函数的导数:
(1)y=(2x-1)4;
(2)y=102x+3;
(3)y=sin4x+cos4x.
解:(1)令u=2x-1,则y=u4,
∴y′x=y′u·u′x=4u3·(2x-1)′=4u3·2
=8(2x-1)3.
(2)令u=2x+3,则y=10u,
∴y′x=y′u·u′x=10u·ln 10·(2x+3)′
=2ln 10·102x+3.
(3)y=sin4x+cos4x
=(sin2x+cos2x)2-2sin2x·cos2x