# 9 13 18 triangle

### Obtuse scalene triangle.

Sides: a = 9   b = 13   c = 18

Area: T = 55.4987747702
Perimeter: p = 40
Semiperimeter: s = 20

Angle ∠ A = α = 28.31663682245° = 28°18'59″ = 0.49442138577 rad
Angle ∠ B = β = 43.24879853748° = 43°14'53″ = 0.75548197396 rad
Angle ∠ C = γ = 108.4365646401° = 108°26'8″ = 1.89325590562 rad

Height: ha = 12.33328328227
Height: hb = 8.53881150311
Height: hc = 6.16664164113

Median: ma = 15.04216089565
Median: mb = 12.65989889012
Median: mc = 6.63332495807

Inradius: r = 2.77548873851
Circumradius: R = 9.48768714822

Vertex coordinates: A[18; 0] B[0; 0] C[6.55655555556; 6.16664164113]
Centroid: CG[8.18551851852; 2.05554721371]
Coordinates of the circumscribed circle: U[9; -33.0001217508]
Coordinates of the inscribed circle: I[7; 2.77548873851]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 151.6843631775° = 151°41'1″ = 0.49442138577 rad
∠ B' = β' = 136.7522014625° = 136°45'7″ = 0.75548197396 rad
∠ C' = γ' = 71.56443535993° = 71°33'52″ = 1.89325590562 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 ### 6. Inradius ### 7. Circumradius ### 8. Calculation of medians #### Look also our friend's collection of math examples and problems:

See more informations about triangles or more information about solving triangles.