# 15 15 21 triangle

### Acute isosceles triangle.

Sides: a = 15   b = 15   c = 21

Area: T = 112.477749775
Perimeter: p = 51
Semiperimeter: s = 25.5

Angle ∠ A = α = 45.57329959992° = 45°34'23″ = 0.79553988302 rad
Angle ∠ B = β = 45.57329959992° = 45°34'23″ = 0.79553988302 rad
Angle ∠ C = γ = 88.85440080016° = 88°51'14″ = 1.55107949932 rad

Height: ha = 14.99769996999
Height: hb = 14.99769996999
Height: hc = 10.71221426428

Median: ma = 16.63658047596
Median: mb = 16.63658047596
Median: mc = 10.71221426428

Inradius: r = 4.41108822647
Circumradius: R = 10.50221006302

Vertex coordinates: A[21; 0] B[0; 0] C[10.5; 10.71221426428]
Centroid: CG[10.5; 3.57107142143]
Coordinates of the circumscribed circle: U[10.5; 0.21100420126]
Coordinates of the inscribed circle: I[10.5; 4.41108822647]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 134.4277004001° = 134°25'37″ = 0.79553988302 rad
∠ B' = β' = 134.4277004001° = 134°25'37″ = 0.79553988302 rad
∠ C' = γ' = 91.14659919984° = 91°8'46″ = 1.55107949932 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.