Question

Find the exact value:
cos (11pi/12) - using half angle identities.

Answer 1

Half Angle Identity for Cosine:
\[Cos(\frac{ a }{ 2 }) = \pm \sqrt{\frac{ 1 + \cos(a) }{ 2 }}\]

Answer 2

To get it to the form (a/2) you must factor out a half so that your new problem looks like this:
\[\cos(\frac{ \frac{ b }{ c } }{ 2 })\]
Where B is the new numerator and C is the new denominator and b/c is your "a" in your identity.

Answer 3

What would be your "a" if you take out a 1/2 from 11pi/12 ?