# 18 18 30 triangle

### Obtuse isosceles triangle.

Sides: a = 18   b = 18   c = 30

Area: T = 149.2488115566
Perimeter: p = 66
Semiperimeter: s = 33

Angle ∠ A = α = 33.55773097619° = 33°33'26″ = 0.58656855435 rad
Angle ∠ B = β = 33.55773097619° = 33°33'26″ = 0.58656855435 rad
Angle ∠ C = γ = 112.8855380476° = 112°53'7″ = 1.97702215667 rad

Height: ha = 16.58331239518
Height: hb = 16.58331239518
Height: hc = 9.95498743711

Median: ma = 23.04334372436
Median: mb = 23.04334372436
Median: mc = 9.95498743711

Inradius: r = 4.52326701687
Circumradius: R = 16.28216126072

Vertex coordinates: A[30; 0] B[0; 0] C[15; 9.95498743711]
Centroid: CG[15; 3.31766247904]
Coordinates of the circumscribed circle: U[15; -6.33217382361]
Coordinates of the inscribed circle: I[15; 4.52326701687]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 146.4432690238° = 146°26'34″ = 0.58656855435 rad
∠ B' = β' = 146.4432690238° = 146°26'34″ = 0.58656855435 rad
∠ C' = γ' = 67.11546195238° = 67°6'53″ = 1.97702215667 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    