A line and a circle intersect at A and B as shown below. Find the distance between A and B.     
 The circle is x^2 + y^2 = 1, and the line is y = x.     
  
 x2 + y2 = 1 is a circle, centered on the origin, and radius 1.    
  
 y = x is a straight line, that passes through the origin.    
  
 Since the straight line passes through the center of the circle,    
 it creates a diameter through the intersection points A and B.    
  
 The radius of the circle is 1, so its diameter is twice that.    
 So, the distance between A & B ( i.e., the diameter ) is 2.    
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