# 18 21 30 triangle

### Obtuse scalene triangle.

Sides: a = 18   b = 21   c = 30

Area: T = 185.9622193738
Perimeter: p = 69
Semiperimeter: s = 34.5

Angle ∠ A = α = 36.18222872212° = 36°10'56″ = 0.63215000429 rad
Angle ∠ B = β = 43.53111521674° = 43°31'52″ = 0.76597619325 rad
Angle ∠ C = γ = 100.2876560611° = 100°17'12″ = 1.75503306782 rad

Height: ha = 20.66224659709
Height: hb = 17.71106851179
Height: hc = 12.39774795826

Median: ma = 24.28796210844
Median: mb = 22.43997767846
Median: mc = 12.5549900398

Inradius: r = 5.39902085142
Circumradius: R = 15.24550341815

Vertex coordinates: A[30; 0] B[0; 0] C[13.05; 12.39774795826]
Centroid: CG[14.35; 4.13224931942]
Coordinates of the circumscribed circle: U[15; -2.72223275324]
Coordinates of the inscribed circle: I[13.5; 5.39902085142]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 143.8187712779° = 143°49'4″ = 0.63215000429 rad
∠ B' = β' = 136.4698847833° = 136°28'8″ = 0.76597619325 rad
∠ C' = γ' = 79.71334393885° = 79°42'48″ = 1.75503306782 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.