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・ Inverse Cost and Quality Law
・ Inverse curve
・ Inverse demand function
・ Inverse distance weighting
・ Inverse distribution
・ Inverse dynamics
・ Inverse electron-demand Diels–Alder reaction
・ Inverse element
・ Inverse exchange-traded fund
・ Inverse Faraday effect
・ Inverse filter
・ Inverse filter (disambiguation)
・ Inverse floating rate note
・ Inverse function
・ Inverse function theorem
Inverse functions and differentiation
・ Inverse Galois problem
・ Inverse gambler's fallacy
・ Inverse gas chromatography
・ Inverse Gaussian distribution
・ Inverse hyperbolic function
・ Inverse image functor
・ Inverse iteration
・ Inverse kinematics
・ Inverse Laplace transform
・ Inverse limit
・ Inverse magnetostrictive effect
・ Inverse mapping theorem
・ Inverse matrix gamma distribution
・ Inverse mean curvature flow


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Inverse functions and differentiation : ウィキペディア英語版
Inverse functions and differentiation

In mathematics, the inverse of a function y = f(x) is a function that, in some fashion, "undoes" the effect of f (see inverse function for a formal and detailed definition). The inverse of f is denoted f^. The statements and are equivalent.
Their two derivatives, assuming they exist, are reciprocal, as the Leibniz notation suggests; that is:
:\frac\,\cdot\, \frac = 1.
This is a direct consequence of the chain rule, since
: \frac\,\cdot\, \frac = \frac
and the derivative of x with respect to x is 1.
Writing explicitly the dependence of y on x and the point at which the differentiation takes place and using Lagrange's notation, the formula for the derivative of the inverse becomes
:\left()'(a)=\frac
Geometrically, a function and inverse function have graphs that are reflections, in the line . This reflection operation turns the gradient of any line into its reciprocal.
Assuming that f has an inverse in a neighbourhood of x and that its derivative at that point is non-zero, its inverse is guaranteed to be differentiable at x and have a derivative given by the above formula.
==Examples==

* \,y = x^2 (for positive x) has inverse x = \sqrt.
: \frac = 2x
\mbox\mbox\mbox\mbox;
\mbox\mbox\mbox\mbox
\frac = \frac
: \frac\,\cdot\,\frac = 2x \cdot\frac = 1.
At , however, there is a problem: the graph of the square root function becomes vertical, corresponding to a horizontal tangent for the square function.
* \,y = e^x (for real x) has inverse \,x = \ln (for positive y)
: \frac = e^x
\mbox\mbox\mbox\mbox;
\mbox\mbox\mbox\mbox
\frac = \frac
: \frac\,\cdot\,\frac = e^x \cdot \frac = \frac = 1

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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