# 3 9 9 triangle

### Acute isosceles triangle.

Sides: a = 3   b = 9   c = 9

Area: T = 13.3111179512
Perimeter: p = 21
Semiperimeter: s = 10.5

Angle ∠ A = α = 19.18881364537° = 19°11'17″ = 0.33548961584 rad
Angle ∠ B = β = 80.40659317731° = 80°24'21″ = 1.40333482476 rad
Angle ∠ C = γ = 80.40659317731° = 80°24'21″ = 1.40333482476 rad

Height: ha = 8.87441196746
Height: hb = 2.95880398915
Height: hc = 2.95880398915

Median: ma = 8.87441196746
Median: mb = 4.97549371855
Median: mc = 4.97549371855

Inradius: r = 1.26877313821
Circumradius: R = 4.56438329755

Vertex coordinates: A[9; 0] B[0; 0] C[0.5; 2.95880398915]
Centroid: CG[3.16766666667; 0.98660132972]
Coordinates of the circumscribed circle: U[4.5; 0.76106388293]
Coordinates of the inscribed circle: I[1.5; 1.26877313821]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 160.8121863546° = 160°48'43″ = 0.33548961584 rad
∠ B' = β' = 99.59440682269° = 99°35'39″ = 1.40333482476 rad
∠ C' = γ' = 99.59440682269° = 99°35'39″ = 1.40333482476 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.