# 21 25 28 triangle

### Acute scalene triangle.

Sides: a = 21   b = 25   c = 28

Area: T = 252.8565690068
Perimeter: p = 74
Semiperimeter: s = 37

Angle ∠ A = α = 46.25767006748° = 46°15'24″ = 0.80773317279 rad
Angle ∠ B = β = 59.32325755274° = 59°19'21″ = 1.03553742637 rad
Angle ∠ C = γ = 74.42107237978° = 74°25'15″ = 1.2998886662 rad

Height: ha = 24.08114942922
Height: hb = 20.22884552055
Height: hc = 18.06111207192

Median: ma = 24.37772434865
Median: mb = 21.36600093633
Median: mc = 18.35875597507

Inradius: r = 6.83439375694
Circumradius: R = 14.534398181

Vertex coordinates: A[28; 0] B[0; 0] C[10.71442857143; 18.06111207192]
Centroid: CG[12.90547619048; 6.02203735731]
Coordinates of the circumscribed circle: U[14; 3.90334122575]
Coordinates of the inscribed circle: I[12; 6.83439375694]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 133.7433299325° = 133°44'36″ = 0.80773317279 rad
∠ B' = β' = 120.6777424473° = 120°40'39″ = 1.03553742637 rad
∠ C' = γ' = 105.5799276202° = 105°34'45″ = 1.2998886662 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    