# 13 13 13 triangle

### Equilateral triangle.

Sides: a = 13   b = 13   c = 13

Area: T = 73.17991466198
Perimeter: p = 39
Semiperimeter: s = 19.5

Angle ∠ A = α = 60° = 1.04771975512 rad
Angle ∠ B = β = 60° = 1.04771975512 rad
Angle ∠ C = γ = 60° = 1.04771975512 rad

Height: ha = 11.25883302492
Height: hb = 11.25883302492
Height: hc = 11.25883302492

Median: ma = 11.25883302492
Median: mb = 11.25883302492
Median: mc = 11.25883302492

Inradius: r = 3.75327767497
Circumradius: R = 7.50655534995

Vertex coordinates: A[13; 0] B[0; 0] C[6.5; 11.25883302492]
Centroid: CG[6.5; 3.75327767497]
Coordinates of the circumscribed circle: U[6.5; 3.75327767497]
Coordinates of the inscribed circle: I[6.5; 3.75327767497]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 120° = 1.04771975512 rad
∠ B' = β' = 120° = 1.04771975512 rad
∠ C' = γ' = 120° = 1.04771975512 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.