# 21 30 30 triangle

### Acute isosceles triangle.

Sides: a = 21   b = 30   c = 30

Area: T = 295.0766155424
Perimeter: p = 81
Semiperimeter: s = 40.5

Angle ∠ A = α = 40.97546302294° = 40°58'29″ = 0.71551422073 rad
Angle ∠ B = β = 69.51326848853° = 69°30'46″ = 1.21332252231 rad
Angle ∠ C = γ = 69.51326848853° = 69°30'46″ = 1.21332252231 rad

Height: ha = 28.10224909928
Height: hb = 19.6721743695
Height: hc = 19.6721743695

Median: ma = 28.10224909928
Median: mb = 21.10768709192
Median: mc = 21.10768709192

Inradius: r = 7.28658309981
Circumradius: R = 16.01328153805

Vertex coordinates: A[30; 0] B[0; 0] C[7.35; 19.6721743695]
Centroid: CG[12.45; 6.55772478983]
Coordinates of the circumscribed circle: U[15; 5.60444853832]
Coordinates of the inscribed circle: I[10.5; 7.28658309981]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 139.0255369771° = 139°1'31″ = 0.71551422073 rad
∠ B' = β' = 110.4877315115° = 110°29'14″ = 1.21332252231 rad
∠ C' = γ' = 110.4877315115° = 110°29'14″ = 1.21332252231 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.