COSH accepts either a COMPLEX or REAL argument and returns a value of the same type. The argument must be specified in radians, regardless of the current trigonometric mode. The real and imaginary parts of COSH(Z) are calculated (using real arithmetic) as
REAL(COSH(Z)) = COSH(REAL(Z))*COS(IMAG(Z))
IMAG(COSH(Z)) = SINH(REAL(Z))*SIN(IMAG(Z))
Notice that intermediate values generated during the calculation of the function can cause over or underflow errors for very large or small values of Z.
