$ c ^2= a ^2+ b ^2$

c ^2= a ^2+ b ^2

$\cos \theta =\displaystyle\frac{ a }{ c }$

cos( theta )= a / c

$\sin \theta =\displaystyle\frac{ b }{ c }$

sin( theta )= b / c

$\tan \theta =\displaystyle\frac{ b }{ a }$

tan( theta )= b / a

$\mbox{cot}\theta=\displaystyle\frac{a}{b}$

cot( theta )= a / b

$\theta=\arccos\displaystyle\frac{a}{c}$

\theta=\arccos\displaystyle\frac{a}{c}

$\theta=\arcsin\displaystyle\frac{b}{c}$

\theta=\arcsin\displaystyle\frac{b}{c}

$\theta=\arctan\displaystyle\frac{b}{a}$

\theta=\arctan\displaystyle\frac{b}{a}

$\theta=\arctan\displaystyle\frac{b}{a}$

\theta=arccot\displaystyle\frac{a}{b}

$\tan\theta=\displaystyle\frac{\sin\theta}{\cos\theta}$

\tan\theta=\displaystyle\frac{\sin\theta}{\cos\theta}

$\sin^2 \theta +\cos^2 \theta =1$

sin( theta )^2+cos( theta )^2=1

$\sin( \alpha + \beta ) =\sin \alpha \cos \beta +\cos \alpha \sin \beta $

sin( alpha + beta )=sin( alpha )*cos( beta )+cos( alpha )*sin( beta )

$\cos( \alpha + \beta )=\cos \alpha \cos \beta +\sin \alpha \sin \beta $

cos( alpha + beta )=cos( alpha )*cos( beta )-sin( alpha )*sin( beta )

$\tan( \alpha + \beta ) =\displaystyle\frac{\tan \alpha -\tan \beta }{1-\tan \alpha \tan \beta }$

tan( alpha + beta )=(tan( alpha )+tan( beta ))/(1 -tan( alpha )*tan( beta ))

$ \theta + \phi =\displaystyle\frac{1}{2} \pi$

theta + phi = pi /2