# 3 21 21 triangle

### Acute isosceles triangle.

Sides: a = 3   b = 21   c = 21

Area: T = 31.42195400985
Perimeter: p = 45
Semiperimeter: s = 22.5

Angle ∠ A = α = 8.19220875163° = 8°11'32″ = 0.14329788998 rad
Angle ∠ B = β = 85.90439562418° = 85°54'14″ = 1.49993068769 rad
Angle ∠ C = γ = 85.90439562418° = 85°54'14″ = 1.49993068769 rad

Height: ha = 20.94663600657
Height: hb = 2.99223371522
Height: hc = 2.99223371522

Median: ma = 20.94663600657
Median: mb = 10.71221426428
Median: mc = 10.71221426428

Inradius: r = 1.39664240044
Circumradius: R = 10.52768886484

Vertex coordinates: A[21; 0] B[0; 0] C[0.21442857143; 2.99223371522]
Centroid: CG[7.07114285714; 0.99774457174]
Coordinates of the circumscribed circle: U[10.5; 0.75219206177]
Coordinates of the inscribed circle: I[1.5; 1.39664240044]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 171.8087912484° = 171°48'28″ = 0.14329788998 rad
∠ B' = β' = 94.09660437582° = 94°5'46″ = 1.49993068769 rad
∠ C' = γ' = 94.09660437582° = 94°5'46″ = 1.49993068769 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.