※ 引述《bitchdog (PEaCE)》之銘言：
: cos(x-y)=ysinx,then y'(x)=?
等號兩邊對 x 微分得
dy dy
(-sin(x-y))(1 - ----) = (----)(sinx) + (y)(cosx)
dx dx
dy dy
(sin(x-y))(----) - sin(x-y) = (sinx)(----) + (y)(cosx)
dx dx
dy
(sin(x-y) - sinx)(----) = (y)(cosx) + sin(x-y)
dx
dy (y)(cosx) + sin(x-y)
---- = ----------------------
dx sin(x-y) - sinx
--
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