# 15 18 18 triangle

### Acute isosceles triangle.

Sides: a = 15   b = 18   c = 18

Area: T = 122.723301129
Perimeter: p = 51
Semiperimeter: s = 25.5

Angle ∠ A = α = 49.24986367043° = 49°14'55″ = 0.86595508626 rad
Angle ∠ B = β = 65.37656816478° = 65°22'32″ = 1.14110208955 rad
Angle ∠ C = γ = 65.37656816478° = 65°22'32″ = 1.14110208955 rad

Height: ha = 16.3633068172
Height: hb = 13.63658901433
Height: hc = 13.63658901433

Median: ma = 16.3633068172
Median: mb = 13.91104277432
Median: mc = 13.91104277432

Inradius: r = 4.81326671094
Circumradius: R = 9.99003437679

Vertex coordinates: A[18; 0] B[0; 0] C[6.25; 13.63658901433]
Centroid: CG[8.08333333333; 4.54552967144]
Coordinates of the circumscribed circle: U[9; 4.12551432366]
Coordinates of the inscribed circle: I[7.5; 4.81326671094]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 130.7511363296° = 130°45'5″ = 0.86595508626 rad
∠ B' = β' = 114.6244318352° = 114°37'28″ = 1.14110208955 rad
∠ C' = γ' = 114.6244318352° = 114°37'28″ = 1.14110208955 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 ### 6. Inradius ### 7. Circumradius ### 8. Calculation of medians #### Look also our friend's collection of math examples and problems:

See more informations about triangles or more information about solving triangles.