Question

`sin(alpha/2) = 1/4` and `405^@ < alpha/2 < 450^@`. Find `cosalpha`"?

Answer is `-(sqrt(8+2sqrt15))/4`.

Thanks in advance!

Answer 1

The interval `(405^@, 450^@)` is the same as the interval:
`(45^@, 90^@)`
`sin (a/2) = 1/4 = 0.25`
Calculator gives --> `a/2 = 14^@47`
The arc (a/2) isn't located in the above interval.
So the question should be corrected before solving.