# 15 15 28 triangle

### Obtuse isosceles triangle.

Sides: a = 15   b = 15   c = 28

Area: T = 75.39223072999
Perimeter: p = 58
Semiperimeter: s = 29

Angle ∠ A = α = 21.03994697813° = 21°2'22″ = 0.36772080206 rad
Angle ∠ B = β = 21.03994697813° = 21°2'22″ = 0.36772080206 rad
Angle ∠ C = γ = 137.9211060437° = 137°55'16″ = 2.40771766125 rad

Height: ha = 10.052230764
Height: hb = 10.052230764
Height: hc = 5.38551648071

Median: ma = 21.17219153597
Median: mb = 21.17219153597
Median: mc = 5.38551648071

Inradius: r = 2.65997347345
Circumradius: R = 20.89107255449

Vertex coordinates: A[28; 0] B[0; 0] C[14; 5.38551648071]
Centroid: CG[14; 1.79550549357]
Coordinates of the circumscribed circle: U[14; -15.50655607378]
Coordinates of the inscribed circle: I[14; 2.65997347345]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 158.9610530219° = 158°57'38″ = 0.36772080206 rad
∠ B' = β' = 158.9610530219° = 158°57'38″ = 0.36772080206 rad
∠ C' = γ' = 42.07989395626° = 42°4'44″ = 2.40771766125 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    