Law Of Cosines Calculator
Calculate side lengths or angles of a triangle using the Law of Cosines. Enter three values (sides and angles) to find the missing one.
Published by:
isCalculator Editorial Team
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How to use this tool?
How to Use the Law of Cosines Calculator
- Enter exactly three values into the fields for sides a, b, c, and angle C (in degrees). Leave the field you want to calculate empty.
- Supported combinations:
- Two sides (a and b) and the included angle C → calculates side c.
- All three sides (a, b, c) → calculates angle C.
- Side a, side c, and angle C → calculates side b.
- Side b, side c, and angle C → calculates side a.
- Units: Use any consistent unit for sides (e.g., meters, inches). Angle C must be in degrees.
- Click Calculate to see the result and the formula used. If the triangle is invalid, an error message will appear.
Tip: Ensure the values satisfy the triangle inequality for valid results.
Previous Results
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Frequently Asked Questions
The Law of Cosines relates the lengths of the sides of a triangle to the cosine of one of its angles: c² = a² + b² - 2ab cos(C).
Use it when you know two sides and the included angle (SAS) or three sides (SSS) of a triangle to find the missing side or angle.
Yes, leave the field you want to find empty and fill in the other three. The calculator supports all combinations where exactly three values are known.
