Solution :
The value of cos 54 degrees is \(\sqrt{10 – 2\sqrt{5}}\over 4\).
Proof :
We know that value of sin 36 degrees is \(\sqrt{10 – 2\sqrt{5}}\over 4\).
Since 54 degree is the complement of 36 degree.
\(\therefore\) cos 54 = sin(90 – 36) = sin 36 = \(\sqrt{10 – 2\sqrt{5}}\over 4\)
Hence, cos 54 degrees is \(\sqrt{10 – 2\sqrt{5}}\over 4\).
