# 9 12 20 triangle

### Obtuse scalene triangle.

Sides: a = 9   b = 12   c = 20

Area: T = 31.65333963423
Perimeter: p = 41
Semiperimeter: s = 20.5

Angle ∠ A = α = 15.29443719921° = 15°17'40″ = 0.26769371483 rad
Angle ∠ B = β = 20.59215995516° = 20°35'30″ = 0.35993912104 rad
Angle ∠ C = γ = 144.1144028456° = 144°6'51″ = 2.51552642949 rad

Height: ha = 7.03440880761
Height: hb = 5.2765566057
Height: hc = 3.16553396342

Median: ma = 15.86766316526
Median: mb = 14.33003496461
Median: mc = 3.53655339059

Inradius: r = 1.54440681143
Circumradius: R = 17.06597806997

Vertex coordinates: A[20; 0] B[0; 0] C[8.425; 3.16553396342]
Centroid: CG[9.475; 1.05551132114]
Coordinates of the circumscribed circle: U[10; -13.82215815854]
Coordinates of the inscribed circle: I[8.5; 1.54440681143]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 164.7065628008° = 164°42'20″ = 0.26769371483 rad
∠ B' = β' = 159.4088400448° = 159°24'30″ = 0.35993912104 rad
∠ C' = γ' = 35.88659715437° = 35°53'9″ = 2.51552642949 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.