# 9 20 28 triangle

### Obtuse scalene triangle.

Sides: a = 9   b = 20   c = 28

Area: T = 48.6599768518
Perimeter: p = 57
Semiperimeter: s = 28.5

Angle ∠ A = α = 9.99554866967° = 9°59'44″ = 0.17444541532 rad
Angle ∠ B = β = 22.6887977061° = 22°41'17″ = 0.39659799003 rad
Angle ∠ C = γ = 147.3176536242° = 147°19' = 2.57111586001 rad

Height: ha = 10.87999485595
Height: hb = 4.86599768518
Height: hc = 3.4711412037

Median: ma = 23.91112944024
Median: mb = 18.23545825288
Median: mc = 6.67108320321

Inradius: r = 1.70552550357
Circumradius: R = 25.92660494118

Vertex coordinates: A[28; 0] B[0; 0] C[8.30435714286; 3.4711412037]
Centroid: CG[12.10111904762; 1.15771373457]
Coordinates of the circumscribed circle: U[14; -21.82110915883]
Coordinates of the inscribed circle: I[8.5; 1.70552550357]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 170.0054513303° = 170°16″ = 0.17444541532 rad
∠ B' = β' = 157.3122022939° = 157°18'43″ = 0.39659799003 rad
∠ C' = γ' = 32.68334637577° = 32°41' = 2.57111586001 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    