# 12 12 21 triangle

### Obtuse isosceles triangle.

Sides: a = 12   b = 12   c = 21

Area: T = 60.99994877028
Perimeter: p = 45
Semiperimeter: s = 22.5

Angle ∠ A = α = 28.95550243719° = 28°57'18″ = 0.50553605103 rad
Angle ∠ B = β = 28.95550243719° = 28°57'18″ = 0.50553605103 rad
Angle ∠ C = γ = 122.0989951256° = 122°5'24″ = 2.1310871633 rad

Height: ha = 10.16765812838
Height: hb = 10.16765812838
Height: hc = 5.80994750193

Median: ma = 16.0165617378
Median: mb = 16.0165617378
Median: mc = 5.80994750193

Inradius: r = 2.71110883423
Circumradius: R = 12.39435467079

Vertex coordinates: A[21; 0] B[0; 0] C[10.5; 5.80994750193]
Centroid: CG[10.5; 1.93664916731]
Coordinates of the circumscribed circle: U[10.5; -6.58440716886]
Coordinates of the inscribed circle: I[10.5; 2.71110883423]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 151.0454975628° = 151°2'42″ = 0.50553605103 rad
∠ B' = β' = 151.0454975628° = 151°2'42″ = 0.50553605103 rad
∠ C' = γ' = 57.91100487437° = 57°54'36″ = 2.1310871633 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.