tan(90∘−α)=cot(α)tan(90∘−α)=bacot(α)=ba⇓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}}}