# 2 20 20 triangle

### Acute isosceles triangle.

Sides: a = 2   b = 20   c = 20

Area: T = 19.97549843554
Perimeter: p = 42
Semiperimeter: s = 21

Angle ∠ A = α = 5.73219679652° = 5°43'55″ = 0.11000417136 rad
Angle ∠ B = β = 87.13440160174° = 87°8'2″ = 1.521077547 rad
Angle ∠ C = γ = 87.13440160174° = 87°8'2″ = 1.521077547 rad

Height: ha = 19.97549843554
Height: hb = 1.99774984355
Height: hc = 1.99774984355

Median: ma = 19.97549843554
Median: mb = 10.10995049384
Median: mc = 10.10995049384

Inradius: r = 0.95111897312
Circumradius: R = 10.01325234864

Vertex coordinates: A[20; 0] B[0; 0] C[0.1; 1.99774984355]
Centroid: CG[6.7; 0.66658328118]
Coordinates of the circumscribed circle: U[10; 0.50106261743]
Coordinates of the inscribed circle: I[1; 0.95111897312]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 174.2688032035° = 174°16'5″ = 0.11000417136 rad
∠ B' = β' = 92.86659839826° = 92°51'58″ = 1.521077547 rad
∠ C' = γ' = 92.86659839826° = 92°51'58″ = 1.521077547 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    