ACOS function
ACOS returns the inverse trigonometric cosine of a number.
Syntax
ACOS (number)
This function returns the inverse trigonometric cosine of number, which is the angle (in radians) whose cosine is number. The angle returned is between 0 and PI.
Example
=ACOS(-1) returns 3.14159265358979 (PI radians).
=DEGREES(ACOS(0.5)) returns 60. The cosine of 60 degrees is 0.5.