1. The problem statement, all variables and given/known data Prove that limh→0[(cos(h-1))/h]=0. 2. Relevant equations Half angle formula From an example: limh→0[(cos(h-1))/h] = limh→0[-(2sin2(h/2))/h] They state that they use the half-angle formula in the following way: cosh= 1-2sin2(h/2) I'm not really sure how they are getting this from the half angle formula. Any pointer in the correct direction would be greatly appreciated. Thank you, in advance.