1) (a ^ 2 - b ^ 2)/(a + b) = 2) ((x - y) ^ 2)/(6x ^ 2 - 6y ^ 2) = 3) (a ^ 2 + 2ab + b ^ 2)/((a + b) ^ 3) : 4) (a ^ 2 - 6a + 9)/(a ^ 2 - 9) =

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