# 18 28 28 triangle

### Acute isosceles triangle.

Sides: a = 18   b = 28   c = 28

Area: T = 238.6277324504
Perimeter: p = 74
Semiperimeter: s = 37

Angle ∠ A = α = 37.4998681694° = 37°29'55″ = 0.65444754607 rad
Angle ∠ B = β = 71.2510659153° = 71°15'2″ = 1.24435585964 rad
Angle ∠ C = γ = 71.2510659153° = 71°15'2″ = 1.24435585964 rad

Height: ha = 26.51441471671
Height: hb = 17.04548088932
Height: hc = 17.04548088932

Median: ma = 26.51441471671
Median: mb = 18.92108879284
Median: mc = 18.92108879284

Inradius: r = 6.44993871488
Circumradius: R = 14.78545600135

Vertex coordinates: A[28; 0] B[0; 0] C[5.78657142857; 17.04548088932]
Centroid: CG[11.26219047619; 5.68216029644]
Coordinates of the circumscribed circle: U[14; 4.75221800043]
Coordinates of the inscribed circle: I[9; 6.44993871488]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 142.5011318306° = 142°30'5″ = 0.65444754607 rad
∠ B' = β' = 108.7499340847° = 108°44'58″ = 1.24435585964 rad
∠ C' = γ' = 108.7499340847° = 108°44'58″ = 1.24435585964 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    