1. The problem statement, all variables and given/known data 2. Relevant equations from the identities found on the internet: [tex]cos(x)=\frac{(e^{ix}+e^{-ix})}{2}[/tex] and [tex]cosh(x)=\frac{(e^{x}+e^{-x})}{2}[/tex] 3. The attempt at a solution Assuming for the definition of cosh(x), if we take x as being equal to (ix), then surely this shows that cosh(x)=cos(x)? Can someone explain why this is wrong please? because i can't see it