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        41. Proposed 
		Problems about congruence of line segments, angles, and triangles. 
     Level: High School, SAT Prep, College geometry. 
    
		  
	 
	
        42. 
		
		
		Ptolemy's Theorem. 
     
		
		  
	 
	
        43.
		Ptolemy's 
		Extension Cyclic Quadrilateral: Ratio of the Diagonals. 
		 
     
		
		  
  
    
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         44. Sangaku 
		Problem
		(An Old Japanese Theorem)
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		Let a convex inscribed polygon be 
		triangulated in any manner, and draw the 
		incircle
        to each triangle so constructed. Then the sum of the 
		inradii
        is a constant independent of the triangulation chosen.
               
 
  
		
  
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         45. Sangaku Problem 2. 
		Proof
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		3  circles of radiii: 
		a,
        b,
         c 
		mutually
         tangent to each other and a  line 
		 
		
                 
  
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                47.
				Sawayama -Thebault's 
				theorem  
     
				
				  
	 
	
                48. 
				
				Semiperimeter and excircles of a triangle 
    
									
									  
	 
	
                49.
				
				Semiperimeter and incircle of a triangle 
    
									
									  
	 
	
                50. 
				
				Semiperimeter and incircle and excircles of a triangle 
    
									
									  
	 
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