GEO007 · Geometry basics · Classes 3–12
Triangle
A triangle has three sides and three angles. The angles always add up to 180°, and any two sides together are longer than the third.
Triangle📐 Formula
Perimeter = a + b + c; Heron: s = (a + b + c)/2, Area = √[s(s − a)(s − b)(s − c)]
✏️ Worked example
Sides 5, 6, 7: s = 9, Area = √(9 × 4 × 3 × 2) = √216 ≈ 14.70.
🌍 Where it is used
Roof trusses, bridges and bicycle frames use triangles because they are rigid.
❓ Quick check
Two angles of a triangle are 50° and 60°. The third angle is…