6 18 18 triangle

Acute isosceles triangle.

Sides: a = 6   b = 18   c = 18

Area: T = 53.24547180479
Perimeter: p = 42
Semiperimeter: s = 21

Angle ∠ A = α = 19.18881364537° = 19°11'17″ = 0.33548961584 rad
Angle ∠ B = β = 80.40659317731° = 80°24'21″ = 1.40333482476 rad
Angle ∠ C = γ = 80.40659317731° = 80°24'21″ = 1.40333482476 rad

Height: ha = 17.74882393493
Height: hb = 5.91660797831
Height: hc = 5.91660797831

Median: ma = 17.74882393493
Median: mb = 9.95498743711
Median: mc = 9.95498743711

Inradius: r = 2.53554627642
Circumradius: R = 9.12876659511

Vertex coordinates: A[18; 0] B[0; 0] C[1; 5.91660797831]
Centroid: CG[6.33333333333; 1.97220265944]
Coordinates of the circumscribed circle: U[9; 1.52112776585]
Coordinates of the inscribed circle: I[3; 2.53554627642]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 160.8121863546° = 160°48'43″ = 0.33548961584 rad
∠ B' = β' = 99.59440682269° = 99°35'39″ = 1.40333482476 rad
∠ C' = γ' = 99.59440682269° = 99°35'39″ = 1.40333482476 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 = 6 ; ; b = 18 ; ; c = 18 ; ;

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

p = a+b+c = 6+18+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 * (21-6)(21-18)(21-18) } ; ; T = sqrt{ 2835 } = 53.24 ; ;

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

T = fraction{ a h _a }{ 2 } ; ; h _a = fraction{ 2 T }{ a } = fraction{ 2 * 53.24 }{ 6 } = 17.75 ; ; h _b = fraction{ 2 T }{ b } = fraction{ 2 * 53.24 }{ 18 } = 5.92 ; ; h _c = fraction{ 2 T }{ c } = fraction{ 2 * 53.24 }{ 18 } = 5.92 ; ;

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{ 6**2-18**2-18**2 }{ 2 * 18 * 18 } ) = 19° 11'17" ; ; beta = arccos( fraction{ b**2-a**2-c**2 }{ 2ac } ) = arccos( fraction{ 18**2-6**2-18**2 }{ 2 * 6 * 18 } ) = 80° 24'21" ; ; gamma = arccos( fraction{ c**2-a**2-b**2 }{ 2ba } ) = arccos( fraction{ 18**2-6**2-18**2 }{ 2 * 18 * 6 } ) = 80° 24'21" ; ;

6. Inradius

T = rs ; ; r = fraction{ T }{ s } = fraction{ 53.24 }{ 21 } = 2.54 ; ;

7. Circumradius

R = fraction{ a }{ 2 * sin( alpha ) } = fraction{ 6 }{ 2 * sin 19° 11'17" } = 9.13 ; ;




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