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Math function
ACOS
Returns the arccosine of a number, in radians.
Rarely usedDifficulty 1250 · ProficientUsage rank #273 of 520
When to use it
Inverse cosine. Returns the angle in radians whose cosine is the argument, between 0 and pi.
The shape of it
- Syntax
=ACOS(number)
Worked examples
Half
=ACOS(0.5) → 1.047197551
Pi over three.
In degrees
=DEGREES(ACOS(0.5)) → 60
In degrees.
Minus one
=ACOS(-1) → 3.141592654
Pi.
Worth knowing
- Angle between two vectors: ACOS(dot product / (length1*length2)).
- Input must be between -1 and 1.
- Wrap in DEGREES for a readable answer.
Where it goes wrong
- #NUM! outside -1 to 1, which happens when a dot-product ratio slips past 1 by rounding; clamp with MIN/MAX.
- Returns radians, not degrees.
Related
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