# 4 21 21 triangle

### Acute isosceles triangle.

Sides: a = 4   b = 21   c = 21

Area: T = 41.80990899207
Perimeter: p = 46
Semiperimeter: s = 23

Angle ∠ A = α = 10.93300475998° = 10°55'48″ = 0.1910765318 rad
Angle ∠ B = β = 84.53549762001° = 84°32'6″ = 1.47554136678 rad
Angle ∠ C = γ = 84.53549762001° = 84°32'6″ = 1.47554136678 rad

Height: ha = 20.90545449604
Height: hb = 3.98218180877
Height: hc = 3.98218180877

Median: ma = 20.90545449604
Median: mb = 10.87442815855
Median: mc = 10.87442815855

Inradius: r = 1.81877865183
Circumradius: R = 10.54879454548

Vertex coordinates: A[21; 0] B[0; 0] C[0.3810952381; 3.98218180877]
Centroid: CG[7.1276984127; 1.32772726959]
Coordinates of the circumscribed circle: U[10.5; 1.00545662338]
Coordinates of the inscribed circle: I[2; 1.81877865183]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 169.07699524° = 169°4'12″ = 0.1910765318 rad
∠ B' = β' = 95.46550237999° = 95°27'54″ = 1.47554136678 rad
∠ C' = γ' = 95.46550237999° = 95°27'54″ = 1.47554136678 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.