**Public Function ACosH( _
ByVal vX As Variant _
) As Variant**

**"Inverse Hyperbolic Cosine" **

Angle whose hyperbolic cosine is X.

Inverse of the CosH function.

**Examples:** ACosH(-10) = 2.99322284612638
ACosH(-2) = 1.31695789692482
ACosH(-1) = 0
ACosH(0) = "0|1.5707963267949"
ACosH(-0.5) = "3.33066907387547E-16|1.0471975511966"
ACosH(1) = 0
ACosH(2) = 1.31695789692482
ACosH(10) = 2.99322284612638
ACosH("2.3|-4.5") = "2.1552640881525|-0.560507402681906"

**See also:** ACos Function
CosH Function
ASinH Function
ATanH Function
ACscH Function
HArccos Function

**vX:** Function returns the principal value of the angle whose hyperbolic cosine (expressed in radians) is vX. Function returns Null if vX is Null or cannot be fixed up to a real or complex number (as defined by the ComplexStringToReals function). Complex numbers are represented within strings as "R|I" where R is the real part and I is the imaginary part.

**Note:** Microsoft named this function HArccos within their Derived Math Function help topic. **Definition:**

Logarithm(Absolute(X) + Sqrt((X - 1) * (X + 1)))

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