# 9 21 21 triangle

### Acute isosceles triangle.

Sides: a = 9   b = 21   c = 21

Area: T = 92.30548617354
Perimeter: p = 51
Semiperimeter: s = 25.5

Angle ∠ A = α = 24.74772502324° = 24°44'50″ = 0.43219209974 rad
Angle ∠ B = β = 77.62663748838° = 77°37'35″ = 1.35548358281 rad
Angle ∠ C = γ = 77.62663748838° = 77°37'35″ = 1.35548358281 rad

Height: ha = 20.51221914968
Height: hb = 8.79109392129
Height: hc = 8.79109392129

Median: ma = 20.51221914968
Median: mb = 12.27880291578
Median: mc = 12.27880291578

Inradius: r = 3.62197984994
Circumradius: R = 10.75497046347

Vertex coordinates: A[21; 0] B[0; 0] C[1.92985714286; 8.79109392129]
Centroid: CG[7.64328571429; 2.9330313071]
Coordinates of the circumscribed circle: U[10.5; 2.3043508136]
Coordinates of the inscribed circle: I[4.5; 3.62197984994]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 155.2532749768° = 155°15'10″ = 0.43219209974 rad
∠ B' = β' = 102.3743625116° = 102°22'25″ = 1.35548358281 rad
∠ C' = γ' = 102.3743625116° = 102°22'25″ = 1.35548358281 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.