# 7 20 20 triangle

### Acute isosceles triangle.

Sides: a = 7   b = 20   c = 20

Area: T = 68.92197903363
Perimeter: p = 47
Semiperimeter: s = 23.5

Angle ∠ A = α = 20.15773162156° = 20°9'26″ = 0.35218115363 rad
Angle ∠ B = β = 79.92113418922° = 79°55'17″ = 1.39548905586 rad
Angle ∠ C = γ = 79.92113418922° = 79°55'17″ = 1.39548905586 rad

Height: ha = 19.69113686675
Height: hb = 6.89219790336
Height: hc = 6.89219790336

Median: ma = 19.69113686675
Median: mb = 11.15879568022
Median: mc = 11.15879568022

Inradius: r = 2.93327570356
Circumradius: R = 10.15767343224

Vertex coordinates: A[20; 0] B[0; 0] C[1.225; 6.89219790336]
Centroid: CG[7.075; 2.29773263445]
Coordinates of the circumscribed circle: U[10; 1.77774285064]
Coordinates of the inscribed circle: I[3.5; 2.93327570356]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 159.8432683784° = 159°50'34″ = 0.35218115363 rad
∠ B' = β' = 100.0798658108° = 100°4'43″ = 1.39548905586 rad
∠ C' = γ' = 100.0798658108° = 100°4'43″ = 1.39548905586 rad

# How did we calculate this triangle?

Now we know the lengths of all three sides of the triangle and the triangle is uniquely determined. Next we calculate another its characteristics - same procedure as calculation of the triangle from the known three sides SSS. ### 1. The triangle circumference is the sum of the lengths of its three sides ### 2. Semiperimeter of the triangle ### 3. The triangle area using Heron's formula ### 4. Calculate the heights of the triangle from its area. ### 5. Calculation of the inner angles of the triangle using a Law of Cosines    