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

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

Answers (1)

2020-10-27
The fromula:
\(\displaystyle{\cos{{\left({x}\right)}}}={\sin{{\left({90}^{\circ}-{x}\right)}}}\)
Substitute the given angle:
\(\displaystyle{\cos{{\left({72}^{\circ}\right)}}}={\sin{{\left({90}^{\circ}-{72}^{\circ}\right)}}}\)
\(\displaystyle{\cos{{\left({72}^{\circ}\right)}}}={\sin{{\left({18}^{\circ}\right)}}}\)
\(\displaystyle=\frac{{\sqrt{{2}}\sqrt{{{3}-\sqrt{{5}}}}}}{{4}}\)
\(\displaystyle\approx{0.30901}\)
0

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