Enter the known measurements; all results update as you type, with the formula and steps.
Formula
c² = a² + b² − 2ab cos C
Worked example
a = 5, b = 7, C = 60°: c = 6.245.
Frequently asked questions
How is it related to Pythagoras?
When C = 90°, cos C = 0 and the formula becomes c² = a² + b².
Can I find angles from three sides?
Yes, rearrange: cos C = (a² + b² − c²) / 2ab.
Which unit for angles?
Degrees.
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Results are estimates for information only. Check important figures with a professional.