# 5 18 21 triangle

### Obtuse scalene triangle.

Sides: a = 5   b = 18   c = 21

Area: T = 38.67881592116
Perimeter: p = 44
Semiperimeter: s = 22

Angle ∠ A = α = 11.80987972119° = 11°48'32″ = 0.2066102392 rad
Angle ∠ B = β = 47.4533334116° = 47°27'12″ = 0.82882169214 rad
Angle ∠ C = γ = 120.7387868672° = 120°44'16″ = 2.10772733402 rad

Height: ha = 15.47112636847
Height: hb = 4.29875732457
Height: hc = 3.68436342106

Median: ma = 19.39771647413
Median: mb = 12.32988280059
Median: mc = 8.01656097709

Inradius: r = 1.7588098146
Circumradius: R = 12.21661966761

Vertex coordinates: A[21; 0] B[0; 0] C[3.3810952381; 3.68436342106]
Centroid: CG[8.1276984127; 1.22878780702]
Coordinates of the circumscribed circle: U[10.5; -6.24438338567]
Coordinates of the inscribed circle: I[4; 1.7588098146]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 168.1911202788° = 168°11'28″ = 0.2066102392 rad
∠ B' = β' = 132.5476665884° = 132°32'48″ = 0.82882169214 rad
∠ C' = γ' = 59.26221313279° = 59°15'44″ = 2.10772733402 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.