# 12 20 25 triangle

### Obtuse scalene triangle.

Sides: a = 12   b = 20   c = 25

Area: T = 118.2799066195
Perimeter: p = 57
Semiperimeter: s = 28.5

Angle ∠ A = α = 28.23767709172° = 28°14'12″ = 0.49328246226 rad
Angle ∠ B = β = 52.04880797108° = 52°2'53″ = 0.90884103603 rad
Angle ∠ C = γ = 99.71551493721° = 99°42'55″ = 1.74403576707 rad

Height: ha = 19.71331776992
Height: hb = 11.82879066195
Height: hc = 9.46223252956

Median: ma = 21.82988799529
Median: mb = 16.86771277934
Median: mc = 10.75987173957

Inradius: r = 4.15501426735
Circumradius: R = 12.6821872188

Vertex coordinates: A[25; 0] B[0; 0] C[7.38; 9.46223252956]
Centroid: CG[10.79333333333; 3.15441084319]
Coordinates of the circumscribed circle: U[12.5; -2.14400659317]
Coordinates of the inscribed circle: I[8.5; 4.15501426735]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 151.7633229083° = 151°45'48″ = 0.49328246226 rad
∠ B' = β' = 127.9521920289° = 127°57'7″ = 0.90884103603 rad
∠ C' = γ' = 80.28548506279° = 80°17'5″ = 1.74403576707 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    