Triangle calculator ASA

Please enter the side of the triangle and two adjacent angles
°
°


Right isosceles triangle.

Sides: a = 2.12113203436   b = 1.5   c = 1.5

Area: T = 1.125
Perimeter: p = 5.12113203436
Semiperimeter: s = 2.56106601718

Angle ∠ A = α = 90° = 1.57107963268 rad
Angle ∠ B = β = 45° = 0.78553981634 rad
Angle ∠ C = γ = 45° = 0.78553981634 rad

Height: ha = 1.06106601718
Height: hb = 1.5
Height: hc = 1.5

Median: ma = 1.06106601718
Median: mb = 1.67770509831
Median: mc = 1.67770509831

Inradius: r = 0.43993398282
Circumradius: R = 1.06106601718

Vertex coordinates: A[1.5; 0] B[0; 0] C[1.5; 1.5]
Centroid: CG[1; 0.5]
Coordinates of the circumscribed circle: U[0.75; 0.75]
Coordinates of the inscribed circle: I[1.06106601718; 0.43993398282]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 90° = 1.57107963268 rad
∠ B' = β' = 135° = 0.78553981634 rad
∠ C' = γ' = 135° = 0.78553981634 rad

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How did we calculate this triangle?

1. Calculate the third unknown inner angle

alpha = 90° ; ; beta = 45° ; ; ; ; alpha + beta + gamma = 180° ; ; ; ; gamma = 180° - alpha - beta = 180° - 90° - 45° = 45° ; ;

2. By using the law of sines, we calculate unknown side a

c = 1.5 ; ; ; ; fraction{ a }{ c } = fraction{ sin( alpha ) }{ sin ( gamma ) } ; ; ; ; a = c * fraction{ sin( alpha ) }{ sin ( gamma ) } ; ; ; ; a = 1.5 * fraction{ sin(90° ) }{ sin (45° ) } = 2.12 ; ;

3. By using the law of sines, we calculate last unknown side b

fraction{ b }{ c } = fraction{ sin( beta ) }{ sin ( gamma ) } ; ; ; ; b = c * fraction{ sin( beta ) }{ sin ( gamma ) } ; ; ; ; b = 1.5 * fraction{ sin(45° ) }{ sin (45° ) } = 1.5 ; ;


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 = 2.12 ; ; b = 1.5 ; ; c = 1.5 ; ;

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

p = a+b+c = 2.12+1.5+1.5 = 5.12 ; ;

5. Semiperimeter of the triangle

s = fraction{ o }{ 2 } = fraction{ 5.12 }{ 2 } = 2.56 ; ;

6. The triangle area using Heron's formula

T = sqrt{ s(s-a)(s-b)(s-c) } ; ; T = sqrt{ 2.56 * (2.56-2.12)(2.56-1.5)(2.56-1.5) } ; ; T = sqrt{ 1.27 } = 1.13 ; ;

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

T = fraction{ a h _a }{ 2 } ; ; h _a = fraction{ 2 T }{ a } = fraction{ 2 * 1.13 }{ 2.12 } = 1.06 ; ; h _b = fraction{ 2 T }{ b } = fraction{ 2 * 1.13 }{ 1.5 } = 1.5 ; ; h _c = fraction{ 2 T }{ c } = fraction{ 2 * 1.13 }{ 1.5 } = 1.5 ; ;

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{ a**2-b**2-c**2 }{ 2bc } ) = arccos( fraction{ 2.12**2-1.5**2-1.5**2 }{ 2 * 1.5 * 1.5 } ) = 90° ; ; beta = arccos( fraction{ b**2-a**2-c**2 }{ 2ac } ) = arccos( fraction{ 1.5**2-2.12**2-1.5**2 }{ 2 * 2.12 * 1.5 } ) = 45° ; ; gamma = arccos( fraction{ c**2-a**2-b**2 }{ 2ba } ) = arccos( fraction{ 1.5**2-2.12**2-1.5**2 }{ 2 * 1.5 * 2.12 } ) = 45° ; ;

9. Inradius

T = rs ; ; r = fraction{ T }{ s } = fraction{ 1.13 }{ 2.56 } = 0.44 ; ;

10. Circumradius

R = fraction{ a }{ 2 * sin( alpha ) } = fraction{ 2.12 }{ 2 * sin 90° } = 1.06 ; ;




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