# 21 21 28 triangle

### Acute isosceles triangle.

Sides: a = 21   b = 21   c = 28

Area: T = 219.1354661795
Perimeter: p = 70
Semiperimeter: s = 35

Angle ∠ A = α = 48.19896851042° = 48°11'23″ = 0.84110686706 rad
Angle ∠ B = β = 48.19896851042° = 48°11'23″ = 0.84110686706 rad
Angle ∠ C = γ = 83.62106297916° = 83°37'14″ = 1.45994553125 rad

Height: ha = 20.876996779
Height: hb = 20.876996779
Height: hc = 15.65224758425

Median: ma = 22.4110934831
Median: mb = 22.4110934831
Median: mc = 15.65224758425

Inradius: r = 6.2610990337
Circumradius: R = 14.08772282582

Vertex coordinates: A[28; 0] B[0; 0] C[14; 15.65224758425]
Centroid: CG[14; 5.21774919475]
Coordinates of the circumscribed circle: U[14; 1.56552475842]
Coordinates of the inscribed circle: I[14; 6.2610990337]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 131.8110314896° = 131°48'37″ = 0.84110686706 rad
∠ B' = β' = 131.8110314896° = 131°48'37″ = 0.84110686706 rad
∠ C' = γ' = 96.37993702084° = 96°22'46″ = 1.45994553125 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.