# 9 18 21 triangle

### Obtuse scalene triangle.

Sides: a = 9   b = 18   c = 21

Area: T = 80.498844719
Perimeter: p = 48
Semiperimeter: s = 24

Angle ∠ A = α = 25.20987652968° = 25°12'32″ = 0.44399759548 rad
Angle ∠ B = β = 58.41218644948° = 58°24'43″ = 1.01994793577 rad
Angle ∠ C = γ = 96.37993702084° = 96°22'46″ = 1.68221373411 rad

Height: ha = 17.889854382
Height: hb = 8.944427191
Height: hc = 7.667651878

Median: ma = 19.03328663107
Median: mb = 13.4166407865
Median: mc = 9.60546863561

Inradius: r = 3.35441019662
Circumradius: R = 10.56554211937

Vertex coordinates: A[21; 0] B[0; 0] C[4.71442857143; 7.667651878]
Centroid: CG[8.57114285714; 2.556550626]
Coordinates of the circumscribed circle: U[10.5; -1.17439356882]
Coordinates of the inscribed circle: I[6; 3.35441019662]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 154.7911234703° = 154°47'28″ = 0.44399759548 rad
∠ B' = β' = 121.5888135505° = 121°35'17″ = 1.01994793577 rad
∠ C' = γ' = 83.62106297916° = 83°37'14″ = 1.68221373411 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.