6.1 Angles and Their Measure/39

$-60^{\circ }\cdot {\frac {\pi }{180^{\circ }}}={\frac {-({\cancel {2}}\cdot {\cancel {2}}\cdot {\cancel {3}}\cdot {\cancel {5}})}{1}}\cdot {\frac {\pi }{{\cancel {2}}\cdot {\cancel {2}}\cdot {\cancel {5}}\cdot {\cancel {3}}\cdot 3}}=-{\frac {\pi }{3}}$