# Solving Trig Function Problem "by hand" (given values, no calculator)

• Aug 6th 2010, 04:48 PM
toinfinity
Solving Trig Function Problem "by hand" (given values, no calculator)
Given sin( π/5 ) = 0.588 and cos ( π/8 ) = 0.924

How can you figure out cos ( 27π/8 )?

I can't think of any trig identities/formulas that would fit the problem. Help please?

But I would suggest having a look at the indentities for $\cos(a+b)$ and $\cos(a-b)$