# 21 21 25 triangle

### Acute isosceles triangle.

Sides: a = 21   b = 21   c = 25

Area: T = 210.9321712884
Perimeter: p = 67
Semiperimeter: s = 33.5

Angle ∠ A = α = 53.47703927703° = 53°28'13″ = 0.93332344062 rad
Angle ∠ B = β = 53.47703927703° = 53°28'13″ = 0.93332344062 rad
Angle ∠ C = γ = 73.05992144595° = 73°3'33″ = 1.27551238412 rad

Height: ha = 20.08987345603
Height: hb = 20.08987345603
Height: hc = 16.87545370307

Median: ma = 20.5610885195
Median: mb = 20.5610885195
Median: mc = 16.87545370307

Inradius: r = 6.29664690413
Circumradius: R = 13.06770251634

Vertex coordinates: A[25; 0] B[0; 0] C[12.5; 16.87545370307]
Centroid: CG[12.5; 5.62548456769]
Coordinates of the circumscribed circle: U[12.5; 3.80875118673]
Coordinates of the inscribed circle: I[12.5; 6.29664690413]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 126.532960723° = 126°31'47″ = 0.93332344062 rad
∠ B' = β' = 126.532960723° = 126°31'47″ = 0.93332344062 rad
∠ C' = γ' = 106.9410785541° = 106°56'27″ = 1.27551238412 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.