# 7 17 21 triangle

### Obtuse scalene triangle.

Sides: a = 7   b = 17   c = 21

Area: T = 53.63994211378
Perimeter: p = 45
Semiperimeter: s = 22.5

Angle ∠ A = α = 17.48876943436° = 17°29'16″ = 0.30552178449 rad
Angle ∠ B = β = 46.86986278687° = 46°52'7″ = 0.81880118722 rad
Angle ∠ C = γ = 115.6443677788° = 115°38'37″ = 2.01883629365 rad

Height: ha = 15.32655488965
Height: hb = 6.31105201339
Height: hc = 5.10985162988

Median: ma = 18.7821639971
Median: mb = 13.14334394281
Median: mc = 7.66548548584

Inradius: r = 2.38439742728
Circumradius: R = 11.64772174149

Vertex coordinates: A[21; 0] B[0; 0] C[4.78657142857; 5.10985162988]
Centroid: CG[8.59552380952; 1.70328387663]
Coordinates of the circumscribed circle: U[10.5; -5.04106024947]
Coordinates of the inscribed circle: I[5.5; 2.38439742728]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 162.5122305656° = 162°30'44″ = 0.30552178449 rad
∠ B' = β' = 133.1311372131° = 133°7'53″ = 0.81880118722 rad
∠ C' = γ' = 64.35663222123° = 64°21'23″ = 2.01883629365 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.