Answer
$$\cos {72^ \circ } \approx 0.30901$$
Work Step by Step
$$\eqalign{
& \cos {72^ \circ } \cr
& {\text{using a calculator to find the value }}\left( {{\text{set the calculator in degree mode}}} \right) \cr
& {\text{then}}{\text{, we obain}} \cr
& \cos {72^ \circ } \approx 0.30901 \cr} $$