ACOS
Returns the arccosine (inverse cosine) of a number. The result is an angle in radians between 0 and PI.
ACOS(number)Arguments
numberThe cosine value, between -1 and 1
=ACOS(0.5)Arccosine of 0.5 = PI/3 radians (60 degrees)
=DEGREES(ACOS(0.5))Convert to degrees: arccosine of 0.5 = 60 degrees
=ACOS(1)Arccosine of 1 = 0 radians (0 degrees)
- •Input must be between -1 and 1
- •Returns radians, wrap in DEGREES() for degrees
- •ACOS is the inverse of COS
- •Passing a value outside the -1 to 1 range to ACOS, which returns a #NUM! error since cosine values only ever fall within that range
- •Expecting ACOS to return an answer in degrees - it always returns radians, so the result often needs to be wrapped in DEGREES to be useful
- •Confusing ACOS with COS - ACOS takes a ratio and returns an angle, while COS takes an angle and returns a ratio, and using the wrong one inverts the intended calculation
COSPerforms the inverse operation - takes an angle and returns a cosine ratio, rather than taking a ratio and returning an angle.ASINCalculates the inverse sine, a related inverse trigonometric function often used alongside ACOS.DEGREESConverts ACOS's radian result into degrees, a common step since ACOS never returns degrees directly.Why does ACOS return a #NUM! error?
The input is outside the valid -1 to 1 range - cosine values, and therefore valid inputs to ACOS, always fall within that range.
Does ACOS return degrees or radians?
Always radians. Wrap the result in DEGREES, like DEGREES(ACOS(0.5)), if you need degrees instead.
What's the difference between ACOS and COS?
ACOS takes a ratio between -1 and 1 and returns the corresponding angle. COS does the opposite - it takes an angle and returns a ratio.
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