I would like to simplify the following expression :
r Cos[γ[t]] + Sqrt[l^2 - r^2/2 + 1/2 r^2 Cos[2 γ[t]]]
by using the mathematical expression :
Cos[2 x]=1 - 2 Sin[x]^2
A similar topic was already created:
However, I would like to use a very simple method for a Mathematica beginner.
May you advice a simple solution to obtain this kind of reduction ?