Question

What is the value of cos 75°?

Answer 1

`(sqrt6-sqrt2)/4`

Explanation:

Apply the trig identity: cos (a + b) = cos a.cos b - sin a.sin b
`cos (75) = cos (30 + 45) = cos 30*cos 45 - sin 30*sin 45 =`
= `(sqrt3/2)(sqrt2/2) - (1/2)(sqrt2/2) = (sqrt6-sqrt2)/4`