Jika tanpa menggunakan kalkulator, nilai cos72°\cos72\degreecos72° adalah ....
5−14\frac{\sqrt{5}-1}{4}45−1
3−12\frac{\sqrt{3}-1}{2}23−1
5+23\frac{\sqrt{5}+2}{3}35+2
5+14\frac{\sqrt{5}+1}{4}45+1
5−23\frac{\sqrt{5}-2}{3}35−2