# 7 15 18 triangle

### Obtuse scalene triangle.

Sides: a = 7   b = 15   c = 18

Area: T = 50.99901951359
Perimeter: p = 40
Semiperimeter: s = 20

Angle ∠ A = α = 22.19216065663° = 22°11'30″ = 0.38773166009 rad
Angle ∠ B = β = 54.03442464357° = 54°2'3″ = 0.94330755091 rad
Angle ∠ C = γ = 103.7744146998° = 103°46'27″ = 1.81112005436 rad

Height: ha = 14.56986271817
Height: hb = 6.79986926848
Height: hc = 5.66655772373

Median: ma = 16.19441347407
Median: mb = 11.41327122105
Median: mc = 7.48333147735

Inradius: r = 2.55495097568
Circumradius: R = 9.26664873853

Vertex coordinates: A[18; 0] B[0; 0] C[4.11111111111; 5.66655772373]
Centroid: CG[7.37703703704; 1.88985257458]
Coordinates of the circumscribed circle: U[9; -2.20663065203]
Coordinates of the inscribed circle: I[5; 2.55495097568]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 157.8088393434° = 157°48'30″ = 0.38773166009 rad
∠ B' = β' = 125.9665753564° = 125°57'57″ = 0.94330755091 rad
∠ C' = γ' = 76.2265853002° = 76°13'33″ = 1.81112005436 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    