Law of cosines calculator
Find a side or angle from the other two sides and the included angle (or three sides).
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Tool guide
Law of cosines calculator: how it works
Practical information to understand the result and use this tool correctly.
About Law of cosines calculator
c² = a² + b² − 2ab cos(C) covers any triangle, not only right-angled ones.
Switch mode to solve for a side (SAS) or an angle (SSS).
When C = 90° the cosine term vanishes and Pythagoras appears.
How to use it
- 1Choose find-side or find-angle mode.
- 2Enter a, b, and either C or c.
- 3Read the result in length or degrees.
Frequently asked questions
- Included angle?
- Angle C must be the angle between sides a and b when finding side c.
- Angle unit?
- Degrees.