Answer
$$4a)\,\,{18^ \circ },\,\,\,4b){\left( {\frac{{360}}{\pi }} \right)^ \circ },\,\,\,\,4c){72^ \circ },\,\,\,\,\,4d){210^ \circ }$$
Work Step by Step
$$\eqalign{
& 4\left( {\text{a}} \right)\,\,\,\frac{\pi }{{10}} \cr
& {\text{Express the angle in degrees}} \cr
& \frac{\pi }{{10}} = \,\,\frac{\pi }{{10}}{\left( {\frac{{180}}{\pi }} \right)^ \circ } \cr
& \,\,\,\,\,\,\, = \,\,{\left( {\frac{{180}}{{10}}} \right)^ \circ } \cr
& \,\,\,\,\,\,\, = \,{18^ \circ } \cr
& \cr
& 4\left( {\text{b}} \right)\,\,2 \cr
& {\text{Express the angle in degrees}} \cr
& 2 = \,2{\left( {\frac{{180}}{\pi }} \right)^ \circ } \cr
& \,\,\,\,\,\,\, = \,{\left( {\frac{{360}}{\pi }} \right)^ \circ } \cr
& \cr
& 4\left( {\text{c}} \right)\,\,\frac{{2\pi }}{5} \cr
& {\text{Express the angle in degrees}} \cr
& \frac{{2\pi }}{5} = \,\,\frac{{2\pi }}{5}{\left( {\frac{{180}}{\pi }} \right)^ \circ } \cr
& \,\,\,\,\,\,\, = \,{\left( {\frac{{360}}{5}} \right)^ \circ } \cr
& \,\,\,\,\,\,\, = {72^ \circ } \cr
& \cr
& 4\left( {\text{d}} \right)\,\,\frac{{7\pi }}{6} \cr
& {\text{Express the angle in degrees}} \cr
& \frac{{7\pi }}{6} = \,\,\frac{{7\pi }}{6}{\left( {\frac{{180}}{\pi }} \right)^ \circ } \cr
& \,\,\,\,\,\,\, = {210^ \circ } \cr} $$
