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This step is not the source of the fallacy.

This step follows from the previous step (y = sqrt(L^2 - x^2)) by differentiating this expression (using the chain rule and the formula for the derivative of the square root function), and doing a little simplification.
Why don't you go back to the list of steps in the proof and see if you can identify which one is wrong, now that you know it isn't this one?
This page last updated: May 26, 1998
Original Web Site Creator / Mathematical Content Developer: Philip Spencer
Current Network Coordinator and Contact Person: Joel Chan - mathnet@math.toronto.edu

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