y=(sin5x)^3 求y'=?
這也是chain rule....
令t=5x
u=sint=sin5x
則y=u^3
dy/dx=d(u^3)/dx
y'=[d(u^3)/du](du/dx)
=[d(u^3)/du][d(sint)/dx]
=[d(u^3)/du][d(sint)/dt](dt/dx)
=[d(u^3)/du][d(sint)/dt][d(5x)/dx]
=3(u^2)(cost)*5 全部代回去...
=15(cos5x)(sin5x)^2
懂了嗎???
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