Question

Question #cc030

Answer 1

`cos 15 = sqrt(2 + sqrt3)/2`

Explanation:

Use trig identity, and trig table:
`2cos^2 (15) = 1 + cos (30) = 1 + sqrt3/2 = (2 + sqrt3)/2`
`cos^2 (15) = (2 + sqrt3)/4`
`cos (15) = +- sqrt(2 + sqrt3)/2`
Since cos 15 is positive, therefore, take the positive value:
`cos (15) = sqrt(2 + sqrt3)/2`