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Thread: No idea how to do this

  1. #1
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    No idea how to do this

    $\displaystyle (x - y)^2 + 13(x - y) + 42$

    Please someone help me or something. I have no idea how to do this at all.
    Like what do I do when its $\displaystyle (x - y)^2$?
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  2. #2
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    Quote Originally Posted by lax600 View Post
    $\displaystyle (x - y)^2 + 13(x - y) + 42$

    Please someone help me or something. I have no idea how to do this at all.
    Like what do I do when its $\displaystyle (x - y)^2$?
    I'm guessing you want to expand this.

    $\displaystyle (x - y)^2 = x^2 - 2xy + y^2$, for starters.
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  3. #3
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    I need to factor it... so I still expand it?
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  4. #4
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    $\displaystyle (x - y)^2 + 13(x - y) + 42$ is about as factored as it gets. One thing you can do:

    $\displaystyle (x - y + 13)(x - y) + 42$
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  5. #5
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    I just asked my dad how to do this and he replys:

    $\displaystyle (x - y)^2 - 13(x - y) + 42$

    if $\displaystyle (x - y)^2 - 14(x - y) + 49$

    $\displaystyle (x - y)^2 - 2*7*(x - y) + 7^2$

    a =$\displaystyle (x - y)^2$
    b =$\displaystyle 7$

    $\displaystyle (x - y)^2 - 13(x - y) + 42
    = [(x - y)^2 - 14(x - y) + 49]
    ={[(x - y) - 7]^2 + [(x - y) - 7]}$
    $\displaystyle =(x - y -7){x - y - 7}
    =(x - y - 7)(x - y - 6)$
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  6. #6
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    Quote Originally Posted by lax600 View Post
    I just asked my dad how to do this and he replys:

    $\displaystyle (x - y)^2 - 13(x - y) + 42$

    if $\displaystyle (x - y)^2 - 14(x - y) + 49$

    $\displaystyle (x - y)^2 - 2*7*(x - y) + 7^2$

    a =$\displaystyle (x - y)^2$
    b =$\displaystyle 7$

    $\displaystyle (x - y)^2 - 13(x - y) + 42
    = [(x - y)^2 - 14(x - y) + 49]
    ={[(x - y) - 7]^2 + [(x - y) - 7]}$
    $\displaystyle =(x - y -7){x - y - 7}
    =(x - y - 7)(x - y - 6)$
    yeah, that's right. Just substitute $\displaystyle t = x-y$ and you have $\displaystyle t^2 - 13t + 42$ which easily factors to $\displaystyle (t - 6)(t - 7)$. I should have been thinking along those lines.
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  7. #7
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    oh
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