# 20 21 21 triangle

### Acute isosceles triangle.

Sides: a = 20   b = 21   c = 21

Area: T = 184.6621853126
Perimeter: p = 62
Semiperimeter: s = 31

Angle ∠ A = α = 56.87437802977° = 56°52'26″ = 0.99326347243 rad
Angle ∠ B = β = 61.56331098511° = 61°33'47″ = 1.07444789647 rad
Angle ∠ C = γ = 61.56331098511° = 61°33'47″ = 1.07444789647 rad

Height: ha = 18.46661853126
Height: hb = 17.58768431549
Height: hc = 17.58768431549

Median: ma = 18.46661853126
Median: mb = 17.61439149538
Median: mc = 17.61439149538

Inradius: r = 5.95768339718
Circumradius: R = 11.94107444617

Vertex coordinates: A[21; 0] B[0; 0] C[9.52438095238; 17.58768431549]
Centroid: CG[10.17546031746; 5.86222810516]
Coordinates of the circumscribed circle: U[10.5; 5.68660687913]
Coordinates of the inscribed circle: I[10; 5.95768339718]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 123.1266219702° = 123°7'34″ = 0.99326347243 rad
∠ B' = β' = 118.4376890149° = 118°26'13″ = 1.07444789647 rad
∠ C' = γ' = 118.4376890149° = 118°26'13″ = 1.07444789647 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.