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Math Help - What's the step after this?

  1. #1
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    What's the step after this?

    x^3 - x - y^3 + y

    x^3 - x - y^3 + y
    = (x^3 - x) - (y^3 - y)<br />
= x(x^2 - 1) - y(y^2 - 1)

    What do I do after this?
    The answer in packet says:
    (x - y)(x^2 + xy + y^2 -1 )
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  2. #2
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    Quote Originally Posted by lax600 View Post
    x^3 - x - y^3 + y

    x^3 - x - y^3 + y
    = (x^3 - x) - (y^3 - y)<br />
= x(x^2 - 1) - y(y^2 - 1)

    What do I do after this?
    The answer in packet says:
    (x - y)(x^2 + xy + y^2 -1 )
    The grouping you've used doesn't cut the mustard. Try this:

    = (x^3 - y^3) - (x - y)

    = (x - y)(x^2 + xy + y^2) - (x - y)

    using difference of two cubes formula

    = ......
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