# 10 20 21 triangle

### Acute scalene triangle.

Sides: a = 10   b = 20   c = 21

Area: T = 98.90662055687
Perimeter: p = 51
Semiperimeter: s = 25.5

Angle ∠ A = α = 28.09880547134° = 28°5'53″ = 0.49904035682 rad
Angle ∠ B = β = 70.38440208646° = 70°23'2″ = 1.22884329049 rad
Angle ∠ C = γ = 81.5187924422° = 81°31'5″ = 1.42327561806 rad

Height: ha = 19.78112411137
Height: hb = 9.89106205569
Height: hc = 9.42196386256

Median: ma = 19.88771818014
Median: mb = 13.05875648572
Median: mc = 11.82215904175

Inradius: r = 3.87986747282
Circumradius: R = 10.61661185131

Vertex coordinates: A[21; 0] B[0; 0] C[3.35771428571; 9.42196386256]
Centroid: CG[8.1199047619; 3.14398795419]
Coordinates of the circumscribed circle: U[10.5; 1.56658774807]
Coordinates of the inscribed circle: I[5.5; 3.87986747282]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 151.9021945287° = 151°54'7″ = 0.49904035682 rad
∠ B' = β' = 109.6165979135° = 109°36'58″ = 1.22884329049 rad
∠ C' = γ' = 98.4822075578° = 98°28'55″ = 1.42327561806 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 ### 6. Inradius ### 7. Circumradius ### 8. Calculation of medians #### Look also our friend's collection of math examples and problems:

See more informations about triangles or more information about solving triangles.