# 8 18 21 triangle

### Obtuse scalene triangle.

Sides: a = 8   b = 18   c = 21

Area: T = 70.77703151046
Perimeter: p = 47
Semiperimeter: s = 23.5

Angle ∠ A = α = 21.99900832984° = 21°59'24″ = 0.38437993563 rad
Angle ∠ B = β = 57.40554616926° = 57°24'20″ = 1.00219143152 rad
Angle ∠ C = γ = 100.6044455009° = 100°36'16″ = 1.75658789821 rad

Height: ha = 17.69325787761
Height: hb = 7.8633368345
Height: hc = 6.744003001

Median: ma = 19.14441897191
Median: mb = 13.09658008537
Median: mc = 9.15215026089

Inradius: r = 3.01215027704
Circumradius: R = 10.68224450178

Vertex coordinates: A[21; 0] B[0; 0] C[4.31095238095; 6.744003001]
Centroid: CG[8.43765079365; 2.247667667]
Coordinates of the circumscribed circle: U[10.5; -1.96658666179]
Coordinates of the inscribed circle: I[5.5; 3.01215027704]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 158.0109916702° = 158°36″ = 0.38437993563 rad
∠ B' = β' = 122.5954538307° = 122°35'40″ = 1.00219143152 rad
∠ C' = γ' = 79.3965544991° = 79°23'44″ = 1.75658789821 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.