# 18 20 21 triangle

### Acute scalene triangle.

Sides: a = 18   b = 20   c = 21

Area: T = 165.5132650574
Perimeter: p = 59
Semiperimeter: s = 29.5

Angle ∠ A = α = 52.01334707109° = 52°48″ = 0.90878063193 rad
Angle ∠ B = β = 61.13112883899° = 61°7'53″ = 1.06769422584 rad
Angle ∠ C = γ = 66.85552408992° = 66°51'19″ = 1.16768440759 rad

Height: ha = 18.39902945082
Height: hb = 16.55112650574
Height: hc = 15.76331095785

Median: ma = 18.42655257727
Median: mb = 16.8087736314
Median: mc = 15.86766316526

Inradius: r = 5.61105983245
Circumradius: R = 11.41990667206

Vertex coordinates: A[21; 0] B[0; 0] C[8.69904761905; 15.76331095785]
Centroid: CG[9.89768253968; 5.25443698595]
Coordinates of the circumscribed circle: U[10.5; 4.48883276138]
Coordinates of the inscribed circle: I[9.5; 5.61105983245]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 127.9876529289° = 127°59'12″ = 0.90878063193 rad
∠ B' = β' = 118.869871161° = 118°52'7″ = 1.06769422584 rad
∠ C' = γ' = 113.1454759101° = 113°8'41″ = 1.16768440759 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.