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Please show me how do you find length of BH or AI (in general), I want both specific proof for this case and in a general case.
My purpose is to try to prove that the area of the square is the same as the area of the parallelogram given two parallel line L1 and L2 and the square and the parallelogram share the same base AB.
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$\begingroup$The area of any parallelogram is base times the height and in your case it is: $AB.BH$ which is the same as the area of the square.
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