# 21 25 25 triangle

### Acute isosceles triangle.

Sides: a = 21   b = 25   c = 25

Area: T = 238.2255077395
Perimeter: p = 71
Semiperimeter: s = 35.5

Angle ∠ A = α = 49.66991749794° = 49°40'9″ = 0.86768906401 rad
Angle ∠ B = β = 65.16554125103° = 65°9'55″ = 1.13773510067 rad
Angle ∠ C = γ = 65.16554125103° = 65°9'55″ = 1.13773510067 rad

Height: ha = 22.68881026091
Height: hb = 19.05880061916
Height: hc = 19.05880061916

Median: ma = 22.68881026091
Median: mb = 19.41100489438
Median: mc = 19.41100489438

Inradius: r = 6.71105655604
Circumradius: R = 13.7743738835

Vertex coordinates: A[25; 0] B[0; 0] C[8.82; 19.05880061916]
Centroid: CG[11.27333333333; 6.35326687305]
Coordinates of the circumscribed circle: U[12.5; 5.78549703107]
Coordinates of the inscribed circle: I[10.5; 6.71105655604]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 130.3310825021° = 130°19'51″ = 0.86768906401 rad
∠ B' = β' = 114.835458749° = 114°50'5″ = 1.13773510067 rad
∠ C' = γ' = 114.835458749° = 114°50'5″ = 1.13773510067 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    