# 5 21 21 triangle

### Acute isosceles triangle.

Sides: a = 5   b = 21   c = 21

Area: T = 52.1276648655
Perimeter: p = 47
Semiperimeter: s = 23.5

Angle ∠ A = α = 13.67442823363° = 13°40'27″ = 0.23986612496 rad
Angle ∠ B = β = 83.16328588319° = 83°9'46″ = 1.4511465702 rad
Angle ∠ C = γ = 83.16328588319° = 83°9'46″ = 1.4511465702 rad

Height: ha = 20.8510659462
Height: hb = 4.9644442729
Height: hc = 4.9644442729

Median: ma = 20.8510659462
Median: mb = 11.07992599031
Median: mc = 11.07992599031

Inradius: r = 2.21881552619
Circumradius: R = 10.57552050865

Vertex coordinates: A[21; 0] B[0; 0] C[0.59552380952; 4.9644442729]
Centroid: CG[7.19884126984; 1.6554814243]
Coordinates of the circumscribed circle: U[10.5; 1.25989529865]
Coordinates of the inscribed circle: I[2.5; 2.21881552619]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 166.3265717664° = 166°19'33″ = 0.23986612496 rad
∠ B' = β' = 96.83771411681° = 96°50'14″ = 1.4511465702 rad
∠ C' = γ' = 96.83771411681° = 96°50'14″ = 1.4511465702 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.