Second derivative formula for curve defined by parametric equations

February 19, 2008

Suppose x and y are defined parametrically by

\displaystyle x = \varphi (t)  \text{ and } y = \psi (t).

Show that

\displaystyle \frac{d^2 y}{dx ^2} = \frac{\varphi '(t) \psi ''(t) - \varphi''(t) \psi '(t)}{\varphi ' (t)^3}.

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