# 10 18 21 triangle

### Obtuse scalene triangle.

Sides: a = 10   b = 18   c = 21

Area: T = 89.98995967733
Perimeter: p = 49
Semiperimeter: s = 24.5

Angle ∠ A = α = 28.40222819014° = 28°24'8″ = 0.49657133343 rad
Angle ∠ B = β = 58.89110774895° = 58°53'28″ = 1.02878432022 rad
Angle ∠ C = γ = 92.70766406091° = 92°42'24″ = 1.61880361171 rad

Height: ha = 17.98799193547
Height: hb = 9.98988440859
Height: hc = 8.56218663594

Median: ma = 18.90876704012
Median: mb = 13.76658998979
Median: mc = 10.08771205009

Inradius: r = 3.66993712969
Circumradius: R = 10.51217267921

Vertex coordinates: A[21; 0] B[0; 0] C[5.16766666667; 8.56218663594]
Centroid: CG[8.72222222222; 2.85439554531]
Coordinates of the circumscribed circle: U[10.5; -0.49663870985]
Coordinates of the inscribed circle: I[6.5; 3.66993712969]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 151.5987718099° = 151°35'52″ = 0.49657133343 rad
∠ B' = β' = 121.1098922511° = 121°6'32″ = 1.02878432022 rad
∠ C' = γ' = 87.29333593909° = 87°17'36″ = 1.61880361171 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.