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Cosine Triangle Calculator

Result

A36.8698976458
B53.1301023542
C90
↗ Math

Cosine Triangle Calculator — free online calculator.

Formula

Method: Validate the three sides, then use the law of cosines to compute angles A and B; set C = 180° − A − B.
  • Cosine Triangle Calculator calculates its result from Side a, Side b, Side c. It uses the formula Calculated with the verified ST Calculator runtime.. Change any input to recalculate the result instantly.
  • The main inputs are Side a, Side b, Side c. Enter them in the units and format shown in the calculator.
  • Keep comparable quantities in compatible units whenever the formula combines or compares them.
  • Changing any input above recalculates the result with the same calculation engine used by this page.

Example: Cosine Triangle

Inputs
  • Side a: 3
  • Side b: 4
  • Side c: 5

Using Side a = 3, Side b = 4, Side c = 5, the calculated result is A: 36.8698976458 | B: 53.1301023542 | C: 90.

Sample result: Calculating…

Frequently asked questions

What does the Cosine Triangle calculate?

Cosine Triangle Calculator — free online calculator.

Which values should I enter?

Enter Side a, Side b, Side c using the units and format shown beside each field.

What formula does this calculator use?

The calculator uses the following relationship: Method: Validate the three sides, then use the law of cosines to compute angles A and B; set C = 180° − A − B..

Why might my result differ from another source?

Results can differ when another source uses different units, rounding rules, conventions or assumptions. Compare the inputs and definitions before comparing results.

Does the result update automatically?

Yes. Changing an input updates the result using the same calculation engine shown on this page.

Page information

Updated: October 7, 2026