# 5 20 21 triangle

### Obtuse scalene triangle.

Sides: a = 5   b = 20   c = 21

Area: T = 49.84397431775
Perimeter: p = 46
Semiperimeter: s = 23

Angle ∠ A = α = 13.72991326754° = 13°43'45″ = 0.24396185686 rad
Angle ∠ B = β = 71.68223015888° = 71°40'56″ = 1.25110921781 rad
Angle ∠ C = γ = 94.58985657358° = 94°35'19″ = 1.65108819068 rad

Height: ha = 19.9365897271
Height: hb = 4.98439743178
Height: hc = 4.74766422074

Median: ma = 20.3533132437
Median: mb = 11.53325625947
Median: mc = 10.11218742081

Inradius: r = 2.16769453555
Circumradius: R = 10.5343762145

Vertex coordinates: A[21; 0] B[0; 0] C[1.57114285714; 4.74766422074]
Centroid: CG[7.52438095238; 1.58222140691]
Coordinates of the circumscribed circle: U[10.5; -0.84327009716]
Coordinates of the inscribed circle: I[3; 2.16769453555]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 166.2710867325° = 166°16'15″ = 0.24396185686 rad
∠ B' = β' = 108.3187698411° = 108°19'4″ = 1.25110921781 rad
∠ C' = γ' = 85.41114342642° = 85°24'41″ = 1.65108819068 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.