# 13 15 21 triangle

### Obtuse scalene triangle.

Sides: a = 13   b = 15   c = 21

Area: T = 96.78993976632
Perimeter: p = 49
Semiperimeter: s = 24.5

Angle ∠ A = α = 37.91882026564° = 37°55'6″ = 0.66217974828 rad
Angle ∠ B = β = 45.16600975216° = 45°9'36″ = 0.78881923923 rad
Angle ∠ C = γ = 96.92216998219° = 96°55'18″ = 1.69216027785 rad

Height: ha = 14.89106765636
Height: hb = 12.90552530218
Height: hc = 9.21880378727

Median: ma = 17.0511392905
Median: mb = 15.77218102956
Median: mc = 9.31439680051

Inradius: r = 3.95105876597
Circumradius: R = 10.57770882423

Vertex coordinates: A[21; 0] B[0; 0] C[9.16766666667; 9.21880378727]
Centroid: CG[10.05655555556; 3.07326792909]
Coordinates of the circumscribed circle: U[10.5; -1.27546747369]
Coordinates of the inscribed circle: I[9.5; 3.95105876597]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 142.0821797344° = 142°4'54″ = 0.66217974828 rad
∠ B' = β' = 134.8439902478° = 134°50'24″ = 0.78881923923 rad
∠ C' = γ' = 83.07883001781° = 83°4'42″ = 1.69216027785 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.