# 11 21 21 triangle

### Acute isosceles triangle.

Sides: a = 11   b = 21   c = 21

Area: T = 111.4688325097
Perimeter: p = 53
Semiperimeter: s = 26.5

Angle ∠ A = α = 30.36662280872° = 30°21'58″ = 0.53299906615 rad
Angle ∠ B = β = 74.81768859564° = 74°49'1″ = 1.3065800996 rad
Angle ∠ C = γ = 74.81768859564° = 74°49'1″ = 1.3065800996 rad

Height: ha = 20.26769681995
Height: hb = 10.61660309616
Height: hc = 10.61660309616

Median: ma = 20.26769681995
Median: mb = 13.06771343454
Median: mc = 13.06771343454

Inradius: r = 4.20663518905
Circumradius: R = 10.88797723384

Vertex coordinates: A[21; 0] B[0; 0] C[2.8810952381; 10.61660309616]
Centroid: CG[7.96603174603; 3.53986769872]
Coordinates of the circumscribed circle: U[10.5; 2.84994641839]
Coordinates of the inscribed circle: I[5.5; 4.20663518905]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 149.6343771913° = 149°38'2″ = 0.53299906615 rad
∠ B' = β' = 105.1833114044° = 105°10'59″ = 1.3065800996 rad
∠ C' = γ' = 105.1833114044° = 105°10'59″ = 1.3065800996 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.