180 ∘ π ⋅ π 2 = 2 ⋅ 2 ⋅ 5 ⋅ 3 ⋅ 3 π = 90 ∘ {\displaystyle {\frac {180^{\circ }}{\pi }}\cdot {\frac {\pi }{\cancel {2}}}={\frac {{\cancel {2}}\cdot {2}\cdot {5}\cdot {3}\cdot {3}}{\pi }}=90^{\circ }}
