# 18 21 28 triangle

### Obtuse scalene triangle.

Sides: a = 18   b = 21   c = 28

Area: T = 188.9440301418
Perimeter: p = 67
Semiperimeter: s = 33.5

Angle ∠ A = α = 39.99900139499° = 39°59'24″ = 0.69879574113 rad
Angle ∠ B = β = 48.57698611237° = 48°34'11″ = 0.84877039938 rad
Angle ∠ C = γ = 91.44401249264° = 91°26'24″ = 1.59659312484 rad

Height: ha = 20.99333668242
Height: hb = 17.99443144208
Height: hc = 13.49657358156

Median: ma = 23.05442837668
Median: mb = 21.06553744329
Median: mc = 13.65765002837

Inradius: r = 5.64400089976
Circumradius: R = 14.00444235144

Vertex coordinates: A[28; 0] B[0; 0] C[11.91107142857; 13.49657358156]
Centroid: CG[13.30435714286; 4.49985786052]
Coordinates of the circumscribed circle: U[14; -0.35219630248]
Coordinates of the inscribed circle: I[12.5; 5.64400089976]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 140.010998605° = 140°36″ = 0.69879574113 rad
∠ B' = β' = 131.4330138876° = 131°25'49″ = 0.84877039938 rad
∠ C' = γ' = 88.56598750736° = 88°33'36″ = 1.59659312484 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.