9 15 18 triangle

Obtuse scalene triangle.

Sides: a = 9   b = 15   c = 18

Area: T = 67.35498329619
Perimeter: p = 42
Semiperimeter: s = 21

Angle ∠ A = α = 29.92664348666° = 29°55'35″ = 0.52223148218 rad
Angle ∠ B = β = 56.25110114041° = 56°15'4″ = 0.98217653566 rad
Angle ∠ C = γ = 93.82325537293° = 93°49'21″ = 1.63875124752 rad

Height: ha = 14.96766295471
Height: hb = 8.98799777283
Height: hc = 7.48333147735

Median: ma = 15.94552187191
Median: mb = 12.09333866224
Median: mc = 8.48552813742

Inradius: r = 3.20771349029
Circumradius: R = 9.02200669145

Vertex coordinates: A[18; 0] B[0; 0] C[5; 7.48333147735]
Centroid: CG[7.66766666667; 2.49444382578]
Coordinates of the circumscribed circle: U[9; -0.60113377943]
Coordinates of the inscribed circle: I[6; 3.20771349029]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 150.0743565133° = 150°4'25″ = 0.52223148218 rad
∠ B' = β' = 123.7498988596° = 123°44'56″ = 0.98217653566 rad
∠ C' = γ' = 86.17774462707° = 86°10'39″ = 1.63875124752 rad

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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.

a = 9 ; ; b = 15 ; ; c = 18 ; ;

1. The triangle circumference is the sum of the lengths of its three sides

p = a+b+c = 9+15+18 = 42 ; ;

2. Semiperimeter of the triangle

s = fraction{ o }{ 2 } = fraction{ 42 }{ 2 } = 21 ; ;

3. The triangle area using Heron's formula

T = sqrt{ s(s-a)(s-b)(s-c) } ; ; T = sqrt{ 21 * (21-9)(21-15)(21-18) } ; ; T = sqrt{ 4536 } = 67.35 ; ;

4. Calculate the heights of the triangle from its area.

T = fraction{ a h _a }{ 2 } ; ; h _a = fraction{ 2 T }{ a } = fraction{ 2 * 67.35 }{ 9 } = 14.97 ; ; h _b = fraction{ 2 T }{ b } = fraction{ 2 * 67.35 }{ 15 } = 8.98 ; ; h _c = fraction{ 2 T }{ c } = fraction{ 2 * 67.35 }{ 18 } = 7.48 ; ;

5. Calculation of the inner angles of the triangle using a Law of Cosines

a**2 = b**2+c**2 - 2bc cos( alpha ) ; ; alpha = arccos( fraction{ a**2-b**2-c**2 }{ 2bc } ) = arccos( fraction{ 9**2-15**2-18**2 }{ 2 * 15 * 18 } ) = 29° 55'35" ; ; beta = arccos( fraction{ b**2-a**2-c**2 }{ 2ac } ) = arccos( fraction{ 15**2-9**2-18**2 }{ 2 * 9 * 18 } ) = 56° 15'4" ; ; gamma = arccos( fraction{ c**2-a**2-b**2 }{ 2ba } ) = arccos( fraction{ 18**2-9**2-15**2 }{ 2 * 15 * 9 } ) = 93° 49'21" ; ;

6. Inradius

T = rs ; ; r = fraction{ T }{ s } = fraction{ 67.35 }{ 21 } = 3.21 ; ;

7. Circumradius

R = fraction{ a }{ 2 * sin( alpha ) } = fraction{ 9 }{ 2 * sin 29° 55'35" } = 9.02 ; ;




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