# 9 18 18 triangle

### Acute isosceles triangle.

Sides: a = 9   b = 18   c = 18

Area: T = 78.42879127607
Perimeter: p = 45
Semiperimeter: s = 22.5

Angle ∠ A = α = 28.95550243719° = 28°57'18″ = 0.50553605103 rad
Angle ∠ B = β = 75.52224878141° = 75°31'21″ = 1.31881160717 rad
Angle ∠ C = γ = 75.52224878141° = 75°31'21″ = 1.31881160717 rad

Height: ha = 17.42884250579
Height: hb = 8.7144212529
Height: hc = 8.7144212529

Median: ma = 17.42884250579
Median: mb = 11.02327038425
Median: mc = 11.02327038425

Inradius: r = 3.48656850116
Circumradius: R = 9.29551600309

Vertex coordinates: A[18; 0] B[0; 0] C[2.25; 8.7144212529]
Centroid: CG[6.75; 2.90547375097]
Coordinates of the circumscribed circle: U[9; 2.32437900077]
Coordinates of the inscribed circle: I[4.5; 3.48656850116]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 151.0454975628° = 151°2'42″ = 0.50553605103 rad
∠ B' = β' = 104.4787512186° = 104°28'39″ = 1.31881160717 rad
∠ C' = γ' = 104.4787512186° = 104°28'39″ = 1.31881160717 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.