standard_description: Prove theorems about triangles. Theorems include: a line parallel to one side of a triangle divides the other two proportionally, and conversely; the Pythagorean Theorem proved using triangle similarity.
problem_activity: Task
Lisa makes an octagon by successively folding a square piece of paper as follows.  First, she folds the square in half vertically and horizontally and also along both diagonals leaving these creases:
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Next, Lisa makes four more folds, identifying each pair of adjacent lines of symmetry for the square used for the folds in the first step:
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Finally Lisa folds the four corners of her shape along the red creases marked below:
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Explain why the shape Lisa has made is a regular octagon.


aligns: no