# 5 5 8 triangle

### Obtuse isosceles triangle.

Sides: a = 5   b = 5   c = 8

Area: T = 12
Perimeter: p = 18
Semiperimeter: s = 9

Angle ∠ A = α = 36.87698976458° = 36°52'12″ = 0.64435011088 rad
Angle ∠ B = β = 36.87698976458° = 36°52'12″ = 0.64435011088 rad
Angle ∠ C = γ = 106.2660204708° = 106°15'37″ = 1.8554590436 rad

Height: ha = 4.8
Height: hb = 4.8
Height: hc = 3

Median: ma = 6.18546584384
Median: mb = 6.18546584384
Median: mc = 3

Inradius: r = 1.33333333333
Circumradius: R = 4.16766666667

Vertex coordinates: A[8; 0] B[0; 0] C[4; 3]
Centroid: CG[4; 1]
Coordinates of the circumscribed circle: U[4; -1.16766666667]
Coordinates of the inscribed circle: I[4; 1.33333333333]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 143.1330102354° = 143°7'48″ = 0.64435011088 rad
∠ B' = β' = 143.1330102354° = 143°7'48″ = 0.64435011088 rad
∠ C' = γ' = 73.74397952917° = 73°44'23″ = 1.8554590436 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    