# 18 25 25 triangle

### Acute isosceles triangle.

Sides: a = 18   b = 25   c = 25

Area: T = 209.9144268214
Perimeter: p = 68
Semiperimeter: s = 34

Angle ∠ A = α = 42.22003920482° = 42°12'1″ = 0.73765357869 rad
Angle ∠ B = β = 68.98998039759° = 68°53'59″ = 1.20325284334 rad
Angle ∠ C = γ = 68.98998039759° = 68°53'59″ = 1.20325284334 rad

Height: ha = 23.32438075794
Height: hb = 16.79331414572
Height: hc = 16.79331414572

Median: ma = 23.32438075794
Median: mb = 17.84395627749
Median: mc = 17.84395627749

Inradius: r = 6.17439490651
Circumradius: R = 13.39883269643

Vertex coordinates: A[25; 0] B[0; 0] C[6.48; 16.79331414572]
Centroid: CG[10.49333333333; 5.59877138191]
Coordinates of the circumscribed circle: U[12.5; 4.82333977071]
Coordinates of the inscribed circle: I[9; 6.17439490651]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 137.8799607952° = 137°47'59″ = 0.73765357869 rad
∠ B' = β' = 111.1100196024° = 111°6'1″ = 1.20325284334 rad
∠ C' = γ' = 111.1100196024° = 111°6'1″ = 1.20325284334 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    