cosh(w+z)= cosh w cosh z + sinh w sinh z
= 0,5 *( ew + e-w )(e^z + e-z )+ 0,5*(e^w -e-w )(e^z -e-z)
= 0,25 ( e^w e^z + e^w e-z + e-w e^z + e-w e-z ) +
(e^w e^z - e^w e-z - e-w e^z + e-w e-z )
=0,25 (2* (e^w e^z) + 2* (e-w e-z ))
=0,25 *2 ( ew+z + e-(w+z) )
=0,5( ew+z + e-(w+z) )
So ?