Arccos (acos) Calculator

x (−1 ≤ x ≤ 1)

θ = arccos(x). Domain: −1 ≤ x ≤ 1. Values outside will be clamped.

Preferred output

Decimals

Formatting only (does not affect internal precision).

Arccos – Quick Cheat Sheet

Definition: θ = arccos(x) is the angle whose cosine is x.
Domain: −1 ≤ x ≤ 1. Range: 0 ≤ θ ≤ π (0° to 180°).
Triangle: x = cos(θ) = adjacent / hypotenuse (right triangle).
Special values: arccos(1)=0°, arccos(0)=90°, arccos(−1)=180°.
Units: 1 rad = 180/π ≈ 57.2958°. Convert with θ° = θ_rad·180/π.
Numerical tip: due to rounding, values slightly outside [−1,1] are clamped.

Related identities

θ = arccos(x) ⇔ x = cos(θ)
arccos(−x) = π − arccos(x)
arccos(x) + arccos(y) = arccos(xy − √((1−x²)(1−y²))) (principal values)

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