# 13 21 26 triangle

### Obtuse scalene triangle.

Sides: a = 13   b = 21   c = 26

Area: T = 135.4999077488
Perimeter: p = 60
Semiperimeter: s = 30

Angle ∠ A = α = 29.75877290681° = 29°45'28″ = 0.51993703502 rad
Angle ∠ B = β = 53.29994290865° = 53°17'58″ = 0.9330250527 rad
Angle ∠ C = γ = 96.94328418454° = 96°56'34″ = 1.69219717764 rad

Height: ha = 20.84660119212
Height: hb = 12.90546740464
Height: hc = 10.42330059606

Median: ma = 22.7211135535
Median: mb = 17.67105970471
Median: mc = 11.66219037897

Inradius: r = 4.51766359163
Circumradius: R = 13.09660301199

Vertex coordinates: A[26; 0] B[0; 0] C[7.76992307692; 10.42330059606]
Centroid: CG[11.25664102564; 3.47443353202]
Coordinates of the circumscribed circle: U[13; -1.58330366079]
Coordinates of the inscribed circle: I[9; 4.51766359163]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 150.2422270932° = 150°14'32″ = 0.51993703502 rad
∠ B' = β' = 126.7010570913° = 126°42'2″ = 0.9330250527 rad
∠ C' = γ' = 83.05771581546° = 83°3'26″ = 1.69219717764 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    