* The arc-cosine of an angle is the inverse of the COS function.
* The "number" is the cosine of an angle in radians.
* If "number" is not numeric, then #VALUE! is returned.
* The angle returned is in radians between 0 and PI.
* If your argument is in degrees, multiply it by PI/180 to convert it to radians.
* If your argument is in radians, multiply it by 180/PI to convert it to degrees.
* If you want to convert the result from radians to degrees, multiply it by 180/PI.
* You can use the DEGREES function to convert from radians to degrees.
* For a working example refer to Trigonometry page.
* For the Microsoft documentation refer to support.office.com.