The Trigonometry of Triangles
To solve any triangle, you generally need to know at least three of its six parameters (3 sides and 3 angles), and at least one of those must be a side length. Knowing only three angles identifies a set of similar triangles but doesn't fix a specific size.
Triangle Classification
Triangles are classified based on their sides and angles:
- Equilateral: All three sides are equal and all angles are 60°.
- Isosceles: Two sides are equal and two angles are equal.
- Scalene: All sides and angles are different.
- Right-angled: One angle is exactly 90°.
- Obtuse: One angle is greater than 90°.
- Acute: All angles are less than 90°.
Heron's Formula for Area
When only the lengths of all three sides are known, Heron's formula is used to calculate the area without needing the height:
Area = √[ s(s-a)(s-b)(s-c) ]
Standard Input Cases:
- • SSS: Known three sides. Always solvable if the sum of two sides > third side.
- • SAS: Two sides and the angle between them. Always solvable.
- • ASA / AAS: Two angles and one side. Always solvable.
- • SSA: The "Ambiguous Case". May result in zero, one, or two valid triangles.
Solving a Right Triangle
In a right triangle, the relationships simplify significantly using SOH CAH TOA:
How to Use This Solver
Input any three values (ensuring at least one is a side) into the configuration panel. The engine will:
- Detect the input case (SSS, SAS, etc.).
- Calculate all missing angles and side lengths.
- Determine the Area and Perimeter.
- Classify the triangle by sides and angles.
- Verify the validity of the inputs using the Triangle Inequality Theorem.