Calculate triangle area, perimeter, angles, and other properties using sides, base & height, or two sides with included angle.
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Calculate all properties of any triangle. Enter three sides, base & height, or two sides with the included angle. Get area, perimeter, all angles, inradius, and circumradius with step-by-step solutions.
A triangle is a polygon with three sides and three angles. The sum of all angles in a triangle is always 180°. Key formulas include Heron's formula for area from three sides, the basic area formula (½ × base × height), and the law of cosines for finding sides and angles.
Heron's Formula
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Heron's formula calculates a triangle's area using only the three side lengths: A = √(s(s-a)(s-b)(s-c)), where s is the semi-perimeter (a+b+c)/2. It's useful when you don't know the height.