# 17 18 21 triangle

### Acute scalene triangle.

Sides: a = 17   b = 18   c = 21

Area: T = 146.8333238744
Perimeter: p = 56
Semiperimeter: s = 28

Angle ∠ A = α = 50.97771974348° = 50°58'38″ = 0.89897199387 rad
Angle ∠ B = β = 55.34554309073° = 55°20'44″ = 0.96659599953 rad
Angle ∠ C = γ = 73.6777371658° = 73°40'39″ = 1.28659127196 rad

Height: ha = 17.27444986757
Height: hb = 16.31548043049
Height: hc = 13.98441179756

Median: ma = 17.61439149538
Median: mb = 16.85222995464
Median: mc = 14.00989257261

Inradius: r = 5.24440442409
Circumradius: R = 10.94109832116

Vertex coordinates: A[21; 0] B[0; 0] C[9.66766666667; 13.98441179756]
Centroid: CG[10.22222222222; 4.66113726585]
Coordinates of the circumscribed circle: U[10.5; 3.07549168503]
Coordinates of the inscribed circle: I[10; 5.24440442409]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 129.0232802565° = 129°1'22″ = 0.89897199387 rad
∠ B' = β' = 124.6554569093° = 124°39'16″ = 0.96659599953 rad
∠ C' = γ' = 106.3232628342° = 106°19'21″ = 1.28659127196 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.