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### 9.6 `ACOS`

— Arccosine function

*Description*:`ACOS(X)`

computes the arccosine of`X`(inverse of`COS(X)`

).*Standard*:Fortran 77 and later, for a complex argument Fortran 2008 or later

*Class*:Elemental function

*Syntax*:`RESULT = ACOS(X)`

*Arguments*:`X`The type shall either be `REAL`

with a magnitude that is less than or equal to one - or the type shall be`COMPLEX`

.*Return value*:The return value is of the same type and kind as

`X`. The real part of the result is in radians and lies in the range*0 \leq \Re \acos(x) \leq \pi*.*Example*:program test_acos real(8) :: x = 0.866_8 x = acos(x) end program test_acos

*Specific names*:Name Argument Return type Standard `ACOS(X)`

`REAL(4) X`

`REAL(4)`

Fortran 77 and later `DACOS(X)`

`REAL(8) X`

`REAL(8)`

Fortran 77 and later *See also*: