Five Fundamental Identities (C)

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The five fundamental identities are

$\begin{displaymath} \cos^2(\theta) + \sin^2(\theta) = 1,\end{displaymath}$

$\begin{displaymath} \cos(-\theta) = \cos(\theta),\end{displaymath}$

$\begin{displaymath} \sin(-\theta) = -\sin(\theta),\end{displaymath}$

$\begin{displaymath} \cos(A+B) = \cos(A)\cos(B)-\sin(A)\sin(B)\end{displaymath}$

and

$\begin{displaymath} \sin(A+B) = \sin(A)\cos(B) + \cos(A)\sin(B).\end{displaymath}$

All the other identities are derived from these five via algebraic manipulations.

Eric S Key
12/30/1999