NAME
    acosh - inverse hyperbolic cosine

SYNOPSIS
    acosh(x [,eps])

TYPES
    x		real, x >= 1
    eps		nonzero real, defaults to epsilon()

    return	nonnegative real

DESCRIPTION
    Returns the cosh of x to a multiple of eps with error less in
    absolute value than .75 * eps.

    acosh(x) = ln(x + sqrt(x^2 - 1)) is the nonnegative real number v
    for which cosh(v) = x.

EXAMPLE
    > print acosh(2, 1e-5), acosh(2, 1e-10), acosh(2, 1e-15), acosh(2, 1e-20)
    1.31696 1.3169578969 1.316957896924817 1.31695789692481670862

LIMITS
    unlike sin and cos, x must be real
    eps > 0

LIBRARY
    NUMBER *qacosh(NUMBER *x, NUMBER *eps)

SEE ALSO
    asinh, atanh, asech, acsch, acoth, epsilon