# 3 8 9 triangle

### Obtuse scalene triangle.

Sides: a = 3   b = 8   c = 9

Area: T = 11.83221595662
Perimeter: p = 20
Semiperimeter: s = 10

Angle ∠ A = α = 19.18881364537° = 19°11'17″ = 0.33548961584 rad
Angle ∠ B = β = 61.21877953194° = 61°13'4″ = 1.06884520891 rad
Angle ∠ C = γ = 99.59440682269° = 99°35'39″ = 1.7388244406 rad

Height: ha = 7.88881063775
Height: hb = 2.95880398915
Height: hc = 2.62993687925

Median: ma = 8.38215273071
Median: mb = 5.38551648071
Median: mc = 4.03111288741

Inradius: r = 1.18332159566
Circumradius: R = 4.56438329755

Vertex coordinates: A[9; 0] B[0; 0] C[1.44444444444; 2.62993687925]
Centroid: CG[3.48114814815; 0.87664562642]
Coordinates of the circumscribed circle: U[4.5; -0.76106388293]
Coordinates of the inscribed circle: I[2; 1.18332159566]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 160.8121863546° = 160°48'43″ = 0.33548961584 rad
∠ B' = β' = 118.7822204681° = 118°46'56″ = 1.06884520891 rad
∠ C' = γ' = 80.40659317731° = 80°24'21″ = 1.7388244406 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    