# 3 18 18 triangle

### Acute isosceles triangle.

Sides: a = 3   b = 18   c = 18

Area: T = 26.9066086672
Perimeter: p = 39
Semiperimeter: s = 19.5

Angle ∠ A = α = 9.56603836944° = 9°33'37″ = 0.16768601732 rad
Angle ∠ B = β = 85.22198081528° = 85°13'11″ = 1.48773662402 rad
Angle ∠ C = γ = 85.22198081528° = 85°13'11″ = 1.48773662402 rad

Height: ha = 17.93773911147
Height: hb = 2.99895651858
Height: hc = 2.99895651858

Median: ma = 17.93773911147
Median: mb = 9.24766210045
Median: mc = 9.24766210045

Inradius: r = 1.38797993165
Circumradius: R = 9.03114137081

Vertex coordinates: A[18; 0] B[0; 0] C[0.25; 2.99895651858]
Centroid: CG[6.08333333333; 0.99765217286]
Coordinates of the circumscribed circle: U[9; 0.7532617809]
Coordinates of the inscribed circle: I[1.5; 1.38797993165]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 170.4439616306° = 170°26'23″ = 0.16768601732 rad
∠ B' = β' = 94.78801918472° = 94°46'49″ = 1.48773662402 rad
∠ C' = γ' = 94.78801918472° = 94°46'49″ = 1.48773662402 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    