What is the value cos(72∘)? Write your answer in decimals.

FizeauV

Answered question

2020-10-26

What is the value $\mathrm{cos}\left({72}^{\circ}\right)$? Write your answer in decimals.

Answer & Explanation

Demi-Leigh Barrera

Skilled2020-10-27Added 97 answers

The formula: $\mathrm{cos}\left(x\right)=\mathrm{sin}({90}^{\circ}-x)$
Substitute the given angle: $\mathrm{cos}\left({72}^{\circ}\right)=\mathrm{sin}({90}^{\circ}-{72}^{\circ})$ $\mathrm{cos}\left({72}^{\circ}\right)=\mathrm{sin}\left({18}^{\circ}\right)$ $=\frac{\sqrt{2}\sqrt{3-\sqrt{5}}}{4}$ $\approx 0.30901$