引用:
原帖由 cwk7093942 於 2014-3-21 09:37 PM 發表
如果你先 make y in terms of x 會更容易搵到 y'
It's not a good idea here.
By taking inverse cos, you have actually restricted the domain.
You are only dealing with a subset of given implicit function.
A simpler example is:
x=y^2
The derivative is dy/dx=1/(2y) and y can be either +ve or -ve.
This is different from y=sqrt(x) and dy/dx=1/[2sqrt(x)], where y must be +ve. (only a subset of the original function)