# 18 26 26 triangle

### Acute isosceles triangle.

Sides: a = 18   b = 26   c = 26

Area: T = 219.5343596518
Perimeter: p = 70
Semiperimeter: s = 35

Angle ∠ A = α = 40.50444934844° = 40°30'16″ = 0.70769367732 rad
Angle ∠ B = β = 69.74877532578° = 69°44'52″ = 1.21773279402 rad
Angle ∠ C = γ = 69.74877532578° = 69°44'52″ = 1.21773279402 rad

Height: ha = 24.39326218353
Height: hb = 16.88771997321
Height: hc = 16.88771997321

Median: ma = 24.39326218353
Median: mb = 18.19334053987
Median: mc = 18.19334053987

Inradius: r = 6.27223884719
Circumradius: R = 13.85766490426

Vertex coordinates: A[26; 0] B[0; 0] C[6.23107692308; 16.88771997321]
Centroid: CG[10.74435897436; 5.62990665774]
Coordinates of the circumscribed circle: U[13; 4.79765323609]
Coordinates of the inscribed circle: I[9; 6.27223884719]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 139.4965506516° = 139°29'44″ = 0.70769367732 rad
∠ B' = β' = 110.2522246742° = 110°15'8″ = 1.21773279402 rad
∠ C' = γ' = 110.2522246742° = 110°15'8″ = 1.21773279402 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    