# 6 6 9 triangle

### Obtuse isosceles triangle.

Sides: a = 6   b = 6   c = 9

Area: T = 17.85988213497
Perimeter: p = 21
Semiperimeter: s = 10.5

Angle ∠ A = α = 41.41096221093° = 41°24'35″ = 0.72327342478 rad
Angle ∠ B = β = 41.41096221093° = 41°24'35″ = 0.72327342478 rad
Angle ∠ C = γ = 97.18107557815° = 97°10'51″ = 1.6966124158 rad

Height: ha = 5.95329404499
Height: hb = 5.95329404499
Height: hc = 3.96986269666

Median: ma = 7.03656236397
Median: mb = 7.03656236397
Median: mc = 3.96986269666

Inradius: r = 1.70108401285
Circumradius: R = 4.53655736761

Vertex coordinates: A[9; 0] B[0; 0] C[4.5; 3.96986269666]
Centroid: CG[4.5; 1.32328756555]
Coordinates of the circumscribed circle: U[4.5; -0.56769467095]
Coordinates of the inscribed circle: I[4.5; 1.70108401285]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 138.5990377891° = 138°35'25″ = 0.72327342478 rad
∠ B' = β' = 138.5990377891° = 138°35'25″ = 0.72327342478 rad
∠ C' = γ' = 82.81992442185° = 82°49'9″ = 1.6966124158 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    