# 18 20 28 triangle

### Obtuse scalene triangle.

Sides: a = 18   b = 20   c = 28

Area: T = 179.3743911147
Perimeter: p = 66
Semiperimeter: s = 33

Angle ∠ A = α = 39.83881498056° = 39°50'17″ = 0.6955306882 rad
Angle ∠ B = β = 45.38216583472° = 45°22'54″ = 0.79220593582 rad
Angle ∠ C = γ = 94.78801918472° = 94°46'49″ = 1.65442264134 rad

Height: ha = 19.93304345718
Height: hb = 17.93773911147
Height: hc = 12.81224222248

Median: ma = 22.60553091109
Median: mb = 21.30772757527
Median: mc = 12.88440987267

Inradius: r = 5.4365573065
Circumradius: R = 14.04988657681

Vertex coordinates: A[28; 0] B[0; 0] C[12.64328571429; 12.81224222248]
Centroid: CG[13.54876190476; 4.27108074083]
Coordinates of the circumscribed circle: U[14; -1.1710738814]
Coordinates of the inscribed circle: I[13; 5.4365573065]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 140.1621850194° = 140°9'43″ = 0.6955306882 rad
∠ B' = β' = 134.6188341653° = 134°37'6″ = 0.79220593582 rad
∠ C' = γ' = 85.22198081528° = 85°13'11″ = 1.65442264134 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.