# 4 9 12 triangle

### Obtuse scalene triangle.

Sides: a = 4   b = 9   c = 12

Area: T = 13.63658901433
Perimeter: p = 25
Semiperimeter: s = 12.5

Angle ∠ A = α = 14.62664748646° = 14°37'35″ = 0.25552801443 rad
Angle ∠ B = β = 34.62221618397° = 34°37'20″ = 0.60442707183 rad
Angle ∠ C = γ = 130.7511363296° = 130°45'5″ = 2.2822041791 rad

Height: ha = 6.81879450716
Height: hb = 3.03301978096
Height: hc = 2.27326483572

Median: ma = 10.4166333328
Median: mb = 7.73298124169
Median: mc = 3.53655339059

Inradius: r = 1.09108712115
Circumradius: R = 7.92202750143

Vertex coordinates: A[12; 0] B[0; 0] C[3.29216666667; 2.27326483572]
Centroid: CG[5.09772222222; 0.75875494524]
Coordinates of the circumscribed circle: U[6; -5.17701795232]
Coordinates of the inscribed circle: I[3.5; 1.09108712115]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 165.3743525135° = 165°22'25″ = 0.25552801443 rad
∠ B' = β' = 145.378783816° = 145°22'40″ = 0.60442707183 rad
∠ C' = γ' = 49.24986367043° = 49°14'55″ = 2.2822041791 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.