# 18 28 30 triangle

### Acute scalene triangle.

Sides: a = 18   b = 28   c = 30

Area: T = 246.5776560119
Perimeter: p = 76
Semiperimeter: s = 38

Angle ∠ A = α = 35.95105676196° = 35°57'2″ = 0.62774557729 rad
Angle ∠ B = β = 65.95879240942° = 65°57'29″ = 1.15111829432 rad
Angle ∠ C = γ = 78.09215082861° = 78°5'29″ = 1.36329539374 rad

Height: ha = 27.39773955688
Height: hb = 17.61326114371
Height: hc = 16.43884373413

Median: ma = 27.58662284483
Median: mb = 20.39660780544
Median: mc = 18.13883571472

Inradius: r = 6.48988568452
Circumradius: R = 15.33299242969

Vertex coordinates: A[30; 0] B[0; 0] C[7.33333333333; 16.43884373413]
Centroid: CG[12.44444444444; 5.47994791138]
Coordinates of the circumscribed circle: U[15; 3.1633317712]
Coordinates of the inscribed circle: I[10; 6.48988568452]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 144.049943238° = 144°2'58″ = 0.62774557729 rad
∠ B' = β' = 114.0422075906° = 114°2'31″ = 1.15111829432 rad
∠ C' = γ' = 101.9088491714° = 101°54'31″ = 1.36329539374 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    