User:Hans G. Oberlack/Sandkiste


Elements

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Base is the square of given side length   with centroid at  
Inscribed are the largest possible circle and right triangle of the same area.

General case

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Segments in the general case

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0) The side length of the base square:  
1) The radius of the inscribed circle:  , see Calculation 1
2) The side length of the inscribed right triangle:  , see Calculation 1

Perimeters in the general case

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0) Perimeter of base square  
1) Perimeter of the inscribed circle:  
2) Perimeter of the inscribed triangle:  

Areas in the general case

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0) Area of the base square  
1) Area of the inscribed circle:  
2) Area of the inscribed triangle:  


Centroids in the general case

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Centroids as graphically displayed

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0) Centroid position of the base square:  
1) Centroid position of the inscribed circle:  , see Calculation 2
2) Centroid position of the inscribed triangle:  , see Calculation 3

Orientated centroids

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The centroid positions of the following shapes will be expressed orientated so that the first shape n with   will be of type   with  . The graphical representation does not correspond to the mathematical expression.
0) Orientated centroid position of the base square:  
1) Orientated centroid position of the inscribed circle:  , see calculation 4
2) Orientated centroid position of the inscribed right triangle:  , see calculation 5

Normalised case

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In the normalised case the area of the base is set to 1.
 

Segments in the normalised case

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0) Side length of the base square:  
1) The radius of the inscribed circle:  
2) The side length of the inscribed right triangle:  

Perimeters in the normalised case

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0) Perimeter of base square  
1) Perimeter of the inscribed circle:  
2) Perimeter of the inscribed triangle:  

Areas in the normalised case

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0) Area of the base square  
1) Area of the inscribed circle:  
2) Area of the inscribed triangle:  

Covered surface of the base shape

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Centroids in the normalised case

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Normalized centroids as graphically displayed

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0) Centroid position of the base square:  
1) Centroid position of the inscribed circle:  
2) Centroid position of the inscribed square:  

Normalized centroids orientated

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The centroid positions of the following shapes will be expressed orientated so that the first shape n with   will be of type   with  . The graphical representation does not correspond to the mathematical expression.
0) Orientated centroid position of the base square:  
1) Orientated centroid position of the inscribed circle:  
2) Orientated centroid position of the inscribed right triangle:  


Calculations

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Equations of given elements and relations

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(0) The area of the right triangle   has to be the same as the area of the circle with radius   around center point  
(1)  since   is a square
(2)  since   is the diagonal of square  
(3)  since   is a right triangle
(4)  since   is a square, because   and   are tangent points of the circle around   with the sides of square  

Calculation 1

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The radius   is calculated:

a) First the relation between   and   is determined from equation (0):
  applying equation (0)
 , definitions of areas of right triangles and circles
 , multiplying both sides by two
 , since negative length cannot be applied

b) Then the relation between   and   is determined from the following identity:
  since   is a square
 , because the three segments are forming the diagonal of the square
 , since   is a right isosceles trinagle
 , applying part a) of the calculation
 , rearranging
 , rearranging
 , because E is a tangent point on the circle and a diagonal side of the triangle  
 , because   is a square with side length  
 , extracting   out of the bracket
 , rearranging

c) Eventually the relation between   and   is determined by using part a) of the calculation:
 , from part a) of the calculation
 , using the result from part b) of the calculation
 , rearranging


Calculation 2

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Calculating the centroid of the inscribed circle as displayed:
 
 
 , since   is collinear to the diagonal of the square
 , since   is half the diagonal of the square
 , rearranging
 , rearranging
 , since   is the diagonal of the square   with side length  
 , rearranging
 , rearranging
 , applying Calculation 1b
 , rearranging
 , rearranging
 , rearranging
 , rearranging

Calculation 3

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Calculating the centroid of the right triangle as displayed:
 
 
 
 , since   is collinear to the diagonal of the square  
 , since   is half the diagonal of the square  
 , rearranging
 , since   is the height of the triangle  
 , since   is the value of the height of the triangle  
 , rearranging
 , since   is collinear to the diagonal of the square  
 , since the centroid of a triangle is a third of the height
 , since the height of a right isoceles triangle with side length a is:  
 , rearranging
 , factoring out
 , rearranging
 , applying result of calculation 1c
 , factoring out
 , factoring out
 , rearranging
 , having a common denominator
 , multiplying into the bracket
 , adding

Calculation 4

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The centroid of the inscribed circle is calculated in orientated expression:
This will be done by rotating the expression as displayed by   which will be done by a   rotation followed by a   rotation
 
 , since  
 , factoring out
 , multiplying
 , applying Calculation 2
 , rearranging
 , multiplying
 , since  
 , adding up
 , factoring out
 

Calculation 5

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The centroid of the inscribed triangle is calculated in orientated expression:
This will be done by rotating the expression as displayed by   which will be done by a   rotation followed by a   rotation
 
 , since  
 , factoring out
 , multiplying
 , applying Calculation 3
 , rearranging
 , multiplying
 , since  
 , adding
 , factoring out
 , reducing