# 20 20 25 triangle

### Acute isosceles triangle.

Sides: a = 20   b = 20   c = 25

Area: T = 195.156618745
Perimeter: p = 65
Semiperimeter: s = 32.5

Angle ∠ A = α = 51.31878125465° = 51°19'4″ = 0.89656647939 rad
Angle ∠ B = β = 51.31878125465° = 51°19'4″ = 0.89656647939 rad
Angle ∠ C = γ = 77.3644374907° = 77°21'52″ = 1.35502630659 rad

Height: ha = 19.5165618745
Height: hb = 19.5165618745
Height: hc = 15.6122494996

Median: ma = 20.31100960116
Median: mb = 20.31100960116
Median: mc = 15.6122494996

Inradius: r = 6.00548057677
Circumradius: R = 12.81102523044

Vertex coordinates: A[25; 0] B[0; 0] C[12.5; 15.6122494996]
Centroid: CG[12.5; 5.20441649987]
Coordinates of the circumscribed circle: U[12.5; 2.80222426916]
Coordinates of the inscribed circle: I[12.5; 6.00548057677]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 128.6822187453° = 128°40'56″ = 0.89656647939 rad
∠ B' = β' = 128.6822187453° = 128°40'56″ = 0.89656647939 rad
∠ C' = γ' = 102.6365625093° = 102°38'8″ = 1.35502630659 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    