Kotangens — qonşu katetin qarşı katetə olan nisbətinə deyilir. İfadəsi: cot α = | A B | | B C | = 1 tan α = cos α sin α {\displaystyle \cot \alpha ={\frac {|AB|}{|BC|}}={\frac {1}{\tan \alpha }}={\frac {\cos \alpha }{\sin \alpha }}} y = cot x {\displaystyle y=\cot x} funksiyasının periodu π − d i r {\displaystyle \pi -dir}
y = cot x {\displaystyle y=\cot x} funskiyası bütün ədəd oxunda azalır
cot ( 90 − α ) = tan α {\displaystyle \cot(90-\alpha )=\tan \alpha }
cot ( 90 + α ) = − tan α {\displaystyle \cot(90+\alpha )=-\tan \alpha }
cot ( 180 − α ) = − cot α {\displaystyle \cot(180-\alpha )=-\cot \alpha }
cot ( 180 + α ) = cot α {\displaystyle \cot(180+\alpha )=\cot \alpha }
cot ( 270 − α ) = tan α {\displaystyle \cot(270-\alpha )=\tan \alpha }
cot ( 270 + α ) = − tan α {\displaystyle \cot(270+\alpha )=-\tan \alpha }
cot ( 360 − α ) = − cot α {\displaystyle \cot(360-\alpha )=-\cot \alpha }
cot ( 360 + α ) = cot α {\displaystyle \cot(360+\alpha )=\cot \alpha }
cot ( α + β ) = 1 − cot α ∗ cot β cot α + cot β {\displaystyle \cot(\alpha +\beta )={\frac {1-\cot \alpha *\cot \beta }{\cot \alpha +\cot \beta }}}
cot ( α − β ) = 1 + cot α ∗ cot β cot α − cot β {\displaystyle \cot(\alpha -\beta )={\frac {1+\cot \alpha *\cot \beta }{\cot \alpha -\cot \beta }}}
cot 2 α = − 1 − cot 2 α 2 cot α {\displaystyle \cot 2\alpha =-{\frac {1-\cot ^{2}\alpha }{2\cot \alpha }}}
cot ( α / 2 ) = sin α 1 − cos α {\displaystyle \cot(\alpha /2)={\frac {\sin \alpha }{1-\cos \alpha }}}
cot ( α / 2 ) = 1 + cos 2 α sin 2 α {\displaystyle \cot(\alpha /2)={\frac {1+\cos 2\alpha }{\sin 2\alpha }}}
cot α + cot β = sin ( α + β ) sin α ∗ sin β {\displaystyle \cot \alpha +\cot \beta ={\frac {\sin(\alpha +\beta )}{\sin \alpha *\sin \beta }}}
cot α − cot β = − sin ( α − β ) sin α ∗ sin β {\displaystyle \cot \alpha -\cot \beta =-{\frac {\sin(\alpha -\beta )}{\sin \alpha *\sin \beta }}}
cot 2 α = 1 + cos 2 α 1 − cos 2 α {\displaystyle \cot ^{2}\alpha ={\frac {1+\cos 2\alpha }{1-\cos 2\alpha }}}
Triqonometrik funksiyalar
funksiyasının periodu 
funskiyası bütün ədəd oxunda azalır
