# 4 18 21 triangle

### Obtuse scalene triangle.

Sides: a = 4   b = 18   c = 21

Area: T = 25.66600370226
Perimeter: p = 43
Semiperimeter: s = 21.5

Angle ∠ A = α = 7.80329967597° = 7°48'11″ = 0.1366187985 rad
Angle ∠ B = β = 37.65884620062° = 37°39'30″ = 0.65772641532 rad
Angle ∠ C = γ = 134.5398541234° = 134°32'19″ = 2.34881405154 rad

Height: ha = 12.83300185113
Height: hb = 2.85111152247
Height: hc = 2.44438130498

Median: ma = 19.45550764583
Median: mb = 12.14549578015
Median: mc = 7.73298124169

Inradius: r = 1.19334900941
Circumradius: R = 14.73110777326

Vertex coordinates: A[21; 0] B[0; 0] C[3.16766666667; 2.44438130498]
Centroid: CG[8.05655555556; 0.81546043499]
Coordinates of the circumscribed circle: U[10.5; -10.3322214243]
Coordinates of the inscribed circle: I[3.5; 1.19334900941]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 172.197700324° = 172°11'49″ = 0.1366187985 rad
∠ B' = β' = 142.3421537994° = 142°20'30″ = 0.65772641532 rad
∠ C' = γ' = 45.46114587659° = 45°27'41″ = 2.34881405154 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.