theorem :: SIN_COS2:27

for p, r being Real holds
( (cosh . p) + (cosh . r) = (2 * (cosh . ((p / 2) + (r / 2)))) * (cosh . ((p / 2) - (r / 2))) & (cosh . p) - (cosh . r) = (2 * (sinh . ((p / 2) - (r / 2)))) * (sinh . ((p / 2) + (r / 2))) )