# 15 17 21 triangle

### Acute scalene triangle.

Sides: a = 15   b = 17   c = 21

Area: T = 126.187711305
Perimeter: p = 53
Semiperimeter: s = 26.5

Angle ∠ A = α = 44.98657265175° = 44°59'9″ = 0.78551490441 rad
Angle ∠ B = β = 53.24437000714° = 53°14'37″ = 0.92992778722 rad
Angle ∠ C = γ = 81.77105734111° = 81°46'14″ = 1.42771657373 rad

Height: ha = 16.82549484067
Height: hb = 14.84655427118
Height: hc = 12.01878202905

Median: ma = 17.57112833908
Median: mb = 16.1487755262
Median: mc = 12.11440414396

Inradius: r = 4.7621777851
Circumradius: R = 10.60992450143

Vertex coordinates: A[21; 0] B[0; 0] C[8.97661904762; 12.01878202905]
Centroid: CG[9.99220634921; 4.00659400968]
Coordinates of the circumscribed circle: U[10.5; 1.51985782079]
Coordinates of the inscribed circle: I[9.5; 4.7621777851]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 135.0144273483° = 135°51″ = 0.78551490441 rad
∠ B' = β' = 126.7566299929° = 126°45'23″ = 0.92992778722 rad
∠ C' = γ' = 98.22994265889° = 98°13'46″ = 1.42771657373 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.