# 7 18 21 triangle

### Obtuse scalene triangle.

Sides: a = 7   b = 18   c = 21

Area: T = 60.66330035524
Perimeter: p = 46
Semiperimeter: s = 23

Angle ∠ A = α = 18.721149202° = 18°43'17″ = 0.32767516766 rad
Angle ∠ B = β = 55.62436862764° = 55°37'25″ = 0.97108164676 rad
Angle ∠ C = γ = 105.6554821704° = 105°39'17″ = 1.84440245093 rad

Height: ha = 17.33222867293
Height: hb = 6.7440333728
Height: hc = 5.77774289098

Median: ma = 19.24218814049
Median: mb = 12.80662484749
Median: mc = 8.73221245983

Inradius: r = 2.63875218936
Circumradius: R = 10.90545045788

Vertex coordinates: A[21; 0] B[0; 0] C[3.95223809524; 5.77774289098]
Centroid: CG[8.31774603175; 1.92658096366]
Coordinates of the circumscribed circle: U[10.5; -2.94224853625]
Coordinates of the inscribed circle: I[5; 2.63875218936]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 161.279850798° = 161°16'43″ = 0.32767516766 rad
∠ B' = β' = 124.3766313724° = 124°22'35″ = 0.97108164676 rad
∠ C' = γ' = 74.34551782964° = 74°20'43″ = 1.84440245093 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.