Triangle calculator VC

Please enter the coordinates of the three vertices


Obtuse scalene triangle.

Sides: a = 13.45436240471   b = 6.70882039325   c = 7.61657731059

Area: T = 16.5
Perimeter: p = 27.77876010854
Semiperimeter: s = 13.88988005427

Angle ∠ A = α = 139.76436416907° = 139°45'49″ = 2.43993357221 rad
Angle ∠ B = β = 18.78986219822° = 18°47'19″ = 0.32879233155 rad
Angle ∠ C = γ = 21.44877363271° = 21°26'52″ = 0.3744333616 rad

Height: ha = 2.45328706826
Height: hb = 4.91993495505
Height: hc = 4.33331122844

Median: ma = 2.5
Median: mb = 10.40443260233
Median: mc = 9.92547166206

Inradius: r = 1.18880075568
Circumradius: R = 10.41439528145

Vertex coordinates: A[0; -3] B[-3; 4] C[6; -6]
Centroid: CG[1; -1.66766666667]
Coordinates of the circumscribed circle: U[0; 0]
Coordinates of the inscribed circle: I[3.49220222125; 1.18880075568]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 40.23663583093° = 40°14'11″ = 2.43993357221 rad
∠ B' = β' = 161.21113780178° = 161°12'41″ = 0.32879233155 rad
∠ C' = γ' = 158.55222636729° = 158°33'8″ = 0.3744333616 rad

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How did we calculate this triangle?

1. We compute side a from coordinates using the Pythagorean theorem

a = |BC| = | beta - gamma | ; ; a**2 = (B_x-C_x)**2 + (B_y-C_y)**2 ; ; a = sqrt{ (B_x-C_x)**2 + (B_y-C_y)**2 } ; ; a = sqrt{ (-3-6)**2 + (4-(-6))**2 } ; ; a = sqrt{ 181 } = 13.45 ; ;

2. We compute side b from coordinates using the Pythagorean theorem

b = |AC| = | alpha - gamma | ; ; b**2 = (A_x-C_x)**2 + (A_y-C_y)**2 ; ; b = sqrt{ (A_x-C_x)**2 + (A_y-C_y)**2 } ; ; b = sqrt{ (0-6)**2 + (-3-(-6))**2 } ; ; b = sqrt{ 45 } = 6.71 ; ;

3. We compute side c from coordinates using the Pythagorean theorem

c = |AB| = | alpha - beta | ; ; c**2 = (A_x-B_x)**2 + (A_y-B_y)**2 ; ; c = sqrt{ (A_x-B_x)**2 + (A_y-B_y)**2 } ; ; c = sqrt{ (0-(-3))**2 + (-3-4)**2 } ; ; c = sqrt{ 58 } = 7.62 ; ;


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 = 13.45 ; ; b = 6.71 ; ; c = 7.62 ; ;

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

p = a+b+c = 13.45+6.71+7.62 = 27.78 ; ;

5. Semiperimeter of the triangle

s = fraction{ o }{ 2 } = fraction{ 27.78 }{ 2 } = 13.89 ; ;

6. The triangle area using Heron's formula

T = sqrt{ s(s-a)(s-b)(s-c) } ; ; T = sqrt{ 13.89 * (13.89-13.45)(13.89-6.71)(13.89-7.62) } ; ; T = sqrt{ 272.25 } = 16.5 ; ;

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

T = fraction{ a h _a }{ 2 } ; ; h _a = fraction{ 2 T }{ a } = fraction{ 2 * 16.5 }{ 13.45 } = 2.45 ; ; h _b = fraction{ 2 T }{ b } = fraction{ 2 * 16.5 }{ 6.71 } = 4.92 ; ; h _c = fraction{ 2 T }{ c } = fraction{ 2 * 16.5 }{ 7.62 } = 4.33 ; ;

8. 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{ b**2+c**2-a**2 }{ 2bc } ) = arccos( fraction{ 6.71**2+7.62**2-13.45**2 }{ 2 * 6.71 * 7.62 } ) = 139° 45'49" ; ; beta = arccos( fraction{ a**2+c**2-b**2 }{ 2ac } ) = arccos( fraction{ 13.45**2+7.62**2-6.71**2 }{ 2 * 13.45 * 7.62 } ) = 18° 47'19" ; ; gamma = 180° - alpha - beta = 180° - 139° 45'49" - 18° 47'19" = 21° 26'52" ; ;

9. Inradius

T = rs ; ; r = fraction{ T }{ s } = fraction{ 16.5 }{ 13.89 } = 1.19 ; ;

10. Circumradius

R = fraction{ a }{ 2 * sin( alpha ) } = fraction{ 13.45 }{ 2 * sin 139° 45'49" } = 10.41 ; ;

11. Calculation of medians

m_a = fraction{ sqrt{ 2 b**2+2c**2 - a**2 } }{ 2 } = fraction{ sqrt{ 2 * 6.71**2+2 * 7.62**2 - 13.45**2 } }{ 2 } = 2.5 ; ; m_b = fraction{ sqrt{ 2 c**2+2a**2 - b**2 } }{ 2 } = fraction{ sqrt{ 2 * 7.62**2+2 * 13.45**2 - 6.71**2 } }{ 2 } = 10.404 ; ; m_c = fraction{ sqrt{ 2 b**2+2a**2 - c**2 } }{ 2 } = fraction{ sqrt{ 2 * 6.71**2+2 * 13.45**2 - 7.62**2 } }{ 2 } = 9.925 ; ;
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