# 5 17 18 triangle

### Obtuse scalene triangle.

Sides: a = 5   b = 17   c = 18

Area: T = 42.42664068712
Perimeter: p = 40
Semiperimeter: s = 20

Angle ∠ A = α = 16.09989339511° = 16°5'56″ = 0.28109794035 rad
Angle ∠ B = β = 70.52987793655° = 70°31'44″ = 1.23109594173 rad
Angle ∠ C = γ = 93.37222866834° = 93°22'20″ = 1.63296538327 rad

Height: ha = 16.97105627485
Height: hb = 4.99113419848
Height: hc = 4.71440452079

Median: ma = 17.32877234512
Median: mb = 10.11218742081
Median: mc = 8.71877978871

Inradius: r = 2.12113203436
Circumradius: R = 9.01656114601

Vertex coordinates: A[18; 0] B[0; 0] C[1.66766666667; 4.71440452079]
Centroid: CG[6.55655555556; 1.57113484026]
Coordinates of the circumscribed circle: U[9; -0.53303300859]
Coordinates of the inscribed circle: I[3; 2.12113203436]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 163.9011066049° = 163°54'4″ = 0.28109794035 rad
∠ B' = β' = 109.4711220634° = 109°28'16″ = 1.23109594173 rad
∠ C' = γ' = 86.62877133166° = 86°37'40″ = 1.63296538327 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    