# 8 17 21 triangle

### Obtuse scalene triangle.

Sides: a = 8   b = 17   c = 21

Area: T = 64.34328317686
Perimeter: p = 46
Semiperimeter: s = 23

Angle ∠ A = α = 21.12986972543° = 21°7'43″ = 0.36987653337 rad
Angle ∠ B = β = 49.99547991151° = 49°59'41″ = 0.87325738534 rad
Angle ∠ C = γ = 108.8776503631° = 108°52'35″ = 1.99002534664 rad

Height: ha = 16.08657079421
Height: hb = 7.5769744914
Height: hc = 6.12878887399

Median: ma = 18.68215416923
Median: mb = 13.42657215821
Median: mc = 8.1399410298

Inradius: r = 2.79875144247
Circumradius: R = 11.09768072181

Vertex coordinates: A[21; 0] B[0; 0] C[5.14328571429; 6.12878887399]
Centroid: CG[8.71442857143; 2.043262958]
Coordinates of the circumscribed circle: U[10.5; -3.59901435117]
Coordinates of the inscribed circle: I[6; 2.79875144247]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 158.8711302746° = 158°52'17″ = 0.36987653337 rad
∠ B' = β' = 130.0055200885° = 130°19″ = 0.87325738534 rad
∠ C' = γ' = 71.12334963694° = 71°7'25″ = 1.99002534664 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.