tan ( 90 ∘ − α ) = cot ( α ) tan ( 90 ∘ − α ) = b a cot ( α ) = b a ⇓ tan ( 90 ∘ − α ) = cot ( α ) {\displaystyle {\begin{aligned}\tan(90^{\circ }-\alpha )=\cot(\alpha )\\\tan(90^{\circ }-\alpha )={\frac {b}{a}}\\\cot(\alpha )={\frac {b}{a}}\\\Downarrow \\\tan(90^{\circ }-\alpha )=\cot(\alpha )\\\end{aligned}}}
