# 12 12 18 triangle

### Obtuse isosceles triangle.

Sides: a = 12   b = 12   c = 18

Area: T = 71.43552853987
Perimeter: p = 42
Semiperimeter: s = 21

Angle ∠ A = α = 41.41096221093° = 41°24'35″ = 0.72327342478 rad
Angle ∠ B = β = 41.41096221093° = 41°24'35″ = 0.72327342478 rad
Angle ∠ C = γ = 97.18107557815° = 97°10'51″ = 1.6966124158 rad

Height: ha = 11.90658808998
Height: hb = 11.90658808998
Height: hc = 7.93772539332

Median: ma = 14.07112472795
Median: mb = 14.07112472795
Median: mc = 7.93772539332

Inradius: r = 3.40216802571
Circumradius: R = 9.07111473522

Vertex coordinates: A[18; 0] B[0; 0] C[9; 7.93772539332]
Centroid: CG[9; 2.64657513111]
Coordinates of the circumscribed circle: U[9; -1.1343893419]
Coordinates of the inscribed circle: I[9; 3.40216802571]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 138.5990377891° = 138°35'25″ = 0.72327342478 rad
∠ B' = β' = 138.5990377891° = 138°35'25″ = 0.72327342478 rad
∠ C' = γ' = 82.81992442185° = 82°49'9″ = 1.6966124158 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.