Question

Can someone help me find what the highlighted part came from?

Answer 1

`\cos(\frac25\pi) = \frac14(\sqrt5-1) \approx 0.3090`

`\sin(\frac25\pi) = \sqrt{\frac58 + (\sqrt5)/(8)} \approx 0.9511`

`\cos(2\pi) = 1`

The value of
`(2\pi )/(5)` radians corresponds to an angle of 180/5 = 72 degrees.