\"\"

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The side lengths of a right triangle are \"\" ; \"a

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Apply Pythagorean theorem: \"a

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\"\"                       (Substitute 7 for b and 25 for c)

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\"\"                     (Evaluate powers: \"\")\"\"

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\"\"     (Subtract 49 from each side)

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\"\"                              (Subtract: \"\")

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 \"\"                      (Take square root to each side)

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\"\"                       (Write \"\")

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\"\"                                 (Cancel square and root)\"\"

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The unknown length of \"\".