# 20 20 21 triangle

### Acute isosceles triangle.

Sides: a = 20   b = 20   c = 21

Area: T = 178.7311467571
Perimeter: p = 61
Semiperimeter: s = 30.5

Angle ∠ A = α = 58.33217567465° = 58°19'54″ = 1.01880812137 rad
Angle ∠ B = β = 58.33217567465° = 58°19'54″ = 1.01880812137 rad
Angle ∠ C = γ = 63.33664865071° = 63°20'11″ = 1.10554302262 rad

Height: ha = 17.87331467571
Height: hb = 17.87331467571
Height: hc = 17.02220445305

Median: ma = 17.903251379
Median: mb = 17.903251379
Median: mc = 17.02220445305

Inradius: r = 5.86600481171
Circumradius: R = 11.74994699089

Vertex coordinates: A[21; 0] B[0; 0] C[10.5; 17.02220445305]
Centroid: CG[10.5; 5.67440148435]
Coordinates of the circumscribed circle: U[10.5; 5.27325746216]
Coordinates of the inscribed circle: I[10.5; 5.86600481171]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 121.6688243254° = 121°40'6″ = 1.01880812137 rad
∠ B' = β' = 121.6688243254° = 121°40'6″ = 1.01880812137 rad
∠ C' = γ' = 116.6643513493° = 116°39'49″ = 1.10554302262 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.