# 21 28 30 triangle

### Acute scalene triangle.

Sides: a = 21   b = 28   c = 30

Area: T = 282.5549884976
Perimeter: p = 79
Semiperimeter: s = 39.5

Angle ∠ A = α = 42.2798724472° = 42°16'43″ = 0.73879029456 rad
Angle ∠ B = β = 63.76443856588° = 63°45'52″ = 1.11328984753 rad
Angle ∠ C = γ = 73.95768898692° = 73°57'25″ = 1.29107912328 rad

Height: ha = 26.91095128549
Height: hb = 20.18221346411
Height: hc = 18.83766589984

Median: ma = 27.05108779894
Median: mb = 21.78330209108
Median: mc = 19.6855019685

Inradius: r = 7.1533161645
Circumradius: R = 15.60878633703

Vertex coordinates: A[30; 0] B[0; 0] C[9.28333333333; 18.83766589984]
Centroid: CG[13.09444444444; 6.27988863328]
Coordinates of the circumscribed circle: U[15; 4.31333976151]
Coordinates of the inscribed circle: I[11.5; 7.1533161645]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 137.7211275528° = 137°43'17″ = 0.73879029456 rad
∠ B' = β' = 116.2365614341° = 116°14'8″ = 1.11328984753 rad
∠ C' = γ' = 106.0433110131° = 106°2'35″ = 1.29107912328 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 ### 6. Inradius ### 7. Circumradius ### 8. Calculation of medians #### Look also our friend's collection of math examples and problems:

See more informations about triangles or more information about solving triangles.