Difference of squares: a2 - b2 =(a + b)(a - b)

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## Calculate and simplify:

 $(a^2-b^2)(a^2+b^2) =$ $(xy+3)(xy-3)(\frac{x^2y^2+9}{2}) =$

## Factorize:

 $x^6-y^2 =$ $(x^3+y)(x^3-y)$ $a^3-ab^2 =$