# 9 20 21 triangle

### Acute scalene triangle.

Sides: a = 9   b = 20   c = 21

Area: T = 89.44327191
Perimeter: p = 50
Semiperimeter: s = 25

Angle ∠ A = α = 25.20987652968° = 25°12'32″ = 0.44399759548 rad
Angle ∠ B = β = 71.17106049117° = 71°10'14″ = 1.24221613863 rad
Angle ∠ C = γ = 83.62106297916° = 83°37'14″ = 1.45994553125 rad

Height: ha = 19.87661598
Height: hb = 8.944427191
Height: hc = 8.51883542

Median: ma = 20.00662490237
Median: mb = 12.68985775404
Median: mc = 11.41327122105

Inradius: r = 3.5787708764
Circumradius: R = 10.56554211937

Vertex coordinates: A[21; 0] B[0; 0] C[2.90547619048; 8.51883542]
Centroid: CG[7.96882539683; 2.83994514]
Coordinates of the circumscribed circle: U[10.5; 1.17439356882]
Coordinates of the inscribed circle: I[5; 3.5787708764]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 154.7911234703° = 154°47'28″ = 0.44399759548 rad
∠ B' = β' = 108.8299395088° = 108°49'46″ = 1.24221613863 rad
∠ C' = γ' = 96.37993702084° = 96°22'46″ = 1.45994553125 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.