设xy-e的X次方=siny确定函数y=f(x).求y的导数.

(-(-e +xy)^x (xy - e log(-e + xy) + xy log(-e+xy))) / (x^2 (-e + xy)^x + e cos(y) - xy cos(y))
用隐函数求导

y' =（ e^x-y）/( x-cosy )

xy - e^x = siny
方程两边对 x 求导得到：
x*y' + y - e^x = y' cosy
==> y' = e^x/( x+cosy )