Calculate the missing side or angle of a triangle using the Law of Cosines.
Inputs
Results
Side c5.2987
Angle C (°)49.00°
Angle A (°)45.41°
Angle B (°)85.59°
About this calculator
About Law of Cosines
The Law of Cosines relates the lengths of the sides of a triangle to the cosine of one of its angles. It generalizes the Pythagorean theorem to non-right triangles.
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Pro Tips
Use when you know two sides and the included angle (SAS).
Use when you know all three sides (SSS) to find an angle.
Ensure angles are in degrees for this calculator.
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Fun Facts
"If angle C is 90°, cos(90°) is 0, reducing the formula to a² + b² = c² (Pythagoras)."
"Euclid proved this geometrically in 'Elements' Book 2, Proposition 12/13."
