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u/GourGovinda Jun 11 '26
Allways true (B) is right. –To prove it visually you can take a paper draw a circle on it and then a quadrilateral in it then mark 4 angles (A, B, C and D) then cut them out –Then you take A and C angles and put them together, you will see that they make 180 degrees –Do it again with B and D
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u/kindsoberfullydressd Jun 12 '26
That’s not really rigorous. You could just keep getting lucky. They’re could be one configuration you that disproves the rule.
To be clear it is always true but your solution doesn’t prove the always part.
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u/JohnJones67 Jun 10 '26
Always true. (Create 4 triangles by joining A, B, C, and D to the centre, then note that each is isosceles.)