# 9 15 21 triangle

### Obtuse scalene triangle.

Sides: a = 9   b = 15   c = 21

Area: T = 58.45767147554
Perimeter: p = 45
Semiperimeter: s = 22.5

Angle ∠ A = α = 21.78767892983° = 21°47'12″ = 0.38802512067 rad
Angle ∠ B = β = 38.21332107017° = 38°12'48″ = 0.66769463445 rad
Angle ∠ C = γ = 120° = 2.09443951024 rad

Height: ha = 12.99903810568
Height: hb = 7.79442286341
Height: hc = 5.56773061672

Median: ma = 17.68547391838
Median: mb = 14.30990880213
Median: mc = 6.53883484153

Inradius: r = 2.59880762114
Circumradius: R = 12.1244355653

Vertex coordinates: A[21; 0] B[0; 0] C[7.07114285714; 5.56773061672]
Centroid: CG[9.35771428571; 1.85657687224]
Coordinates of the circumscribed circle: U[10.5; -6.06221778265]
Coordinates of the inscribed circle: I[7.5; 2.59880762114]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 158.2133210702° = 158°12'48″ = 0.38802512067 rad
∠ B' = β' = 141.7876789298° = 141°47'12″ = 0.66769463445 rad
∠ C' = γ' = 60° = 2.09443951024 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.