# 20 20 26 triangle

### Acute isosceles triangle.

Sides: a = 20   b = 20   c = 26

Area: T = 197.5832893996
Perimeter: p = 66
Semiperimeter: s = 33

Angle ∠ A = α = 49.45883981265° = 49°27'30″ = 0.86332118901 rad
Angle ∠ B = β = 49.45883981265° = 49°27'30″ = 0.86332118901 rad
Angle ∠ C = γ = 81.0833203747° = 81°5' = 1.41551688735 rad

Height: ha = 19.75882893996
Height: hb = 19.75882893996
Height: hc = 15.19986841536

Median: ma = 20.92884495365
Median: mb = 20.92884495365
Median: mc = 15.19986841536

Inradius: r = 5.98773604241
Circumradius: R = 13.15990338992

Vertex coordinates: A[26; 0] B[0; 0] C[13; 15.19986841536]
Centroid: CG[13; 5.06662280512]
Coordinates of the circumscribed circle: U[13; 2.04396502544]
Coordinates of the inscribed circle: I[13; 5.98773604241]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 130.5421601874° = 130°32'30″ = 0.86332118901 rad
∠ B' = β' = 130.5421601874° = 130°32'30″ = 0.86332118901 rad
∠ C' = γ' = 98.9176796253° = 98°55' = 1.41551688735 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    