# 7 9 12 triangle

### Obtuse scalene triangle.

Sides: a = 7   b = 9   c = 12

Area: T = 31.3054951685
Perimeter: p = 28
Semiperimeter: s = 14

Angle ∠ A = α = 35.43109446873° = 35°25'51″ = 0.61883866419 rad
Angle ∠ B = β = 48.19896851042° = 48°11'23″ = 0.84110686706 rad
Angle ∠ C = γ = 96.37993702084° = 96°22'46″ = 1.68221373411 rad

Height: ha = 8.944427191
Height: hb = 6.957665593
Height: hc = 5.21774919475

Median: ma = 10.01224921973
Median: mb = 8.73221245983
Median: mc = 5.38551648071

Inradius: r = 2.23660679775
Circumradius: R = 6.03773835392

Vertex coordinates: A[12; 0] B[0; 0] C[4.66766666667; 5.21774919475]
Centroid: CG[5.55655555556; 1.73991639825]
Coordinates of the circumscribed circle: U[6; -0.67108203932]
Coordinates of the inscribed circle: I[5; 2.23660679775]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 144.5699055313° = 144°34'9″ = 0.61883866419 rad
∠ B' = β' = 131.8110314896° = 131°48'37″ = 0.84110686706 rad
∠ C' = γ' = 83.62106297916° = 83°37'14″ = 1.68221373411 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    