# 12 21 30 triangle

### Obtuse scalene triangle.

Sides: a = 12   b = 21   c = 30

Area: T = 98.35987184748
Perimeter: p = 63
Semiperimeter: s = 31.5

Angle ∠ A = α = 18.19548723388° = 18°11'42″ = 0.31875604293 rad
Angle ∠ B = β = 33.12329402077° = 33°7'23″ = 0.57881043646 rad
Angle ∠ C = γ = 128.6822187453° = 128°40'56″ = 2.24659278597 rad

Height: ha = 16.39331197458
Height: hb = 9.36774969976
Height: hc = 6.55772478983

Median: ma = 25.18992834356
Median: mb = 20.29216238877
Median: mc = 8.21658383626

Inradius: r = 3.12224989992
Circumradius: R = 19.21553784566

Vertex coordinates: A[30; 0] B[0; 0] C[10.05; 6.55772478983]
Centroid: CG[13.35; 2.18657492994]
Coordinates of the circumscribed circle: U[15; -12.01096115354]
Coordinates of the inscribed circle: I[10.5; 3.12224989992]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 161.8055127661° = 161°48'18″ = 0.31875604293 rad
∠ B' = β' = 146.8777059792° = 146°52'37″ = 0.57881043646 rad
∠ C' = γ' = 51.31878125465° = 51°19'4″ = 2.24659278597 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.