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Module · Math · Geometry
Triangle Calculator
Given three sides (SSS), compute the three angles, area (Heron's formula), perimeter and classify the triangle.
Enter three sides
∠A
36.87°
∠B
53.13°
∠C
90.00°
Area
6
Perimeter
12
Right triangle
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Guide
How Triangle Calculator works
Step 01
Enter three sides
A, B, C — any triangle where the sum of any two sides exceeds the third.
Step 02
See angles
Angles A, B, C computed via law of cosines; they sum to 180°.
Step 03
See area + type
Area via Heron's formula; classification is equilateral, isosceles, scalene or right.
FAQ
Frequently asked
Why does it say 'invalid triangle'?+
The triangle inequality: the sum of any two sides must be strictly greater than the third. Otherwise no triangle exists.
Which method computes the angles?+
Law of cosines: cos(A) = (b² + c² − a²) / (2bc).