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Properties of a triangle formulas

16 formulas for Properties of a triangle, from the Trigonometry section of the Quantix formula library. Tap 🧮 next to a formula to solve it for any variable with step-by-step working.

NameFormulaNote
Angle sumA + B + C = π 🧮 Solve step by step
Sine rulea/sin A = b/sin B = c/sin C = 2R 🧮 Solve step by stepR circumradius
Cosine rulea² = b² + c² − 2bc cos A 🧮 Solve step by step
Cosine rule (angle)cos A = (b² + c² − a²) / 2bc 🧮 Solve step by step
Projection rulea = b cos C + c cos B 🧮 Solve step by step
Tangent (Napier) ruletan((B − C)/2) = ((b − c)/(b + c)) cot(A/2) 🧮 Solve step by step
AreaΔ = ½ bc sin A 🧮 Solve step by step
Heron's formulaΔ = √(s(s−a)(s−b)(s−c)), s = (a+b+c)/2 🧮 Solve step by step
CircumradiusR = abc / 4Δ 🧮 Solve step by step
Inradiusr = Δ / s = 4R sin(A/2) sin(B/2) sin(C/2) 🧮 Solve step by step
Exradiusr₁ = Δ / (s − a) 🧮 Solve step by step
Half-angle (sides)sin(A/2) = √((s−b)(s−c)/bc) 🧮 Solve step by step
Half-angle (sides)cos(A/2) = √(s(s−a)/bc) 🧮 Solve step by step
In any triangletan A + tan B + tan C = tan A tan B tan C 🧮 Solve step by step
In any trianglesin 2A + sin 2B + sin 2C = 4 sin A sin B sin C 🧮 Solve step by step
Median lengthmₐ = ½ √(2b² + 2c² − a²) 🧮 Solve step by step

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Related: Trigonometry