# 9 11 18 triangle

### Obtuse scalene triangle.

Sides: a = 9   b = 11   c = 18

Area: T = 38.98771773792
Perimeter: p = 38
Semiperimeter: s = 19

Angle ∠ A = α = 23.192176951° = 23°11'30″ = 0.40547727373 rad
Angle ∠ B = β = 28.77218565328° = 28°46'19″ = 0.50221636284 rad
Angle ∠ C = γ = 128.0366373957° = 128°2'11″ = 2.23546562879 rad

Height: ha = 8.66438171954
Height: hb = 7.08985777053
Height: hc = 4.33219085977

Median: ma = 14.22114626533
Median: mb = 13.12444047484
Median: mc = 4.4722135955

Inradius: r = 2.05219567042
Circumradius: R = 11.42768338963

Vertex coordinates: A[18; 0] B[0; 0] C[7.88988888889; 4.33219085977]
Centroid: CG[8.63296296296; 1.44439695326]
Coordinates of the circumscribed circle: U[9; -7.04107764412]
Coordinates of the inscribed circle: I[8; 2.05219567042]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 156.808823049° = 156°48'30″ = 0.40547727373 rad
∠ B' = β' = 151.2288143467° = 151°13'41″ = 0.50221636284 rad
∠ C' = γ' = 51.96436260429° = 51°57'49″ = 2.23546562879 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    