# 11 18 18 triangle

### Acute isosceles triangle.

Sides: a = 11   b = 18   c = 18

Area: T = 94.26552507555
Perimeter: p = 47
Semiperimeter: s = 23.5

Angle ∠ A = α = 35.5833181146° = 35°34'59″ = 0.62110436693 rad
Angle ∠ B = β = 72.2088409427° = 72°12'30″ = 1.26602744921 rad
Angle ∠ C = γ = 72.2088409427° = 72°12'30″ = 1.26602744921 rad

Height: ha = 17.1399136501
Height: hb = 10.47439167506
Height: hc = 10.47439167506

Median: ma = 17.1399136501
Median: mb = 11.89553772534
Median: mc = 11.89553772534

Inradius: r = 4.01112872662
Circumradius: R = 9.45220514491

Vertex coordinates: A[18; 0] B[0; 0] C[3.36111111111; 10.47439167506]
Centroid: CG[7.12203703704; 3.49113055835]
Coordinates of the circumscribed circle: U[9; 2.88881268317]
Coordinates of the inscribed circle: I[5.5; 4.01112872662]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 144.4176818854° = 144°25'1″ = 0.62110436693 rad
∠ B' = β' = 107.7921590573° = 107°47'30″ = 1.26602744921 rad
∠ C' = γ' = 107.7921590573° = 107°47'30″ = 1.26602744921 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    