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Cosine Triangle Calculator
Use the law of cosines to find the third side and angles of a triangle.
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Side c
Compare Your Options And Get Clear Answers
Use the law of cosines to find the third side and angles of a triangle.
Cosine Triangle Estimator
Enter your numbers below for an instant estimate.
0
💡 Tip: c2 = a2 + b2 – 2ab cos C.
How It Works
Key concepts behind this calculator
1
Enter Values
Fill in each field with your own numbers.
2
Calculate
Results update as you change the inputs.
3
Review
Read the breakdown and the explanation.
4
Adjust
Change values to compare scenarios.
Quick Reference Guide
Cosine Quick Guide
Typical values for reference.
| a | b | C deg | Side c |
|---|---|---|---|
| 5 | 7 | 60 | 6.245 |
| 3 | 4 | 90 | 5.000 |
| 10 | 10 | 60 | 10.000 |
| 8 | 5 | 120 | 11.358 |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
Common Questions
Cosine Triangle Calculator FAQ
Answers to common questions about this calculator.
c2 = a2 + b2 – 2ab cos C.
When you know two sides and the included angle, or all three sides.
It reduces to Pythagoras.
Yes, rearrange for each angle.