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    Sorry if this is reaaaaaaally easy but my mind's just gone blank so yeah. XD

    I'm stuck on this question about solving simultaneous equations with substituition...

    x² + y² = 64
    y = 2x + 8

    What i've done so far is:

    x² + (2x + 8)² = 64
    x² + (2x + 8)(2x + 8) = 64

    (2x + 8)(2x + 8) = 4x² + 16x + 16x + 64 = 64

    so

    x² + 4x² + 32x + 64 = 64
    5x² + 32x + 0 = 0

    Now I'm stuck. How do I get that into brackets so i can work out x? D:
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    You can factorise out the x. So you have

    x(5x+32)=0

    So either x=0 or 5x+32=0.

    Can you do it now?
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    5x^2+32x=0

    x(5x+32)=0

    x=0 or x=\frac{-32}{5}
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    If you don't immediately see anything, you can always use the quadratic formula

    I'll put it below just for your convenience

    x= \frac{-b \pm \sqrt{b^2-4ac}}{2a}

    By the way, if you're not sure what this is, then you probably haven't done this yet.
    In this case, thomaskurian89's post would probably be more for you :woo:
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    (Original post by 0-))
    You can factorise out the x. So you have

    x(5x+32)=0

    So either x=0 or 5x+32=0.

    Can you do it now?
    Omg im such an idiot, ty for help!!
    In the end i got y = 8 or y = -4.8
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    (Original post by placenta medicae talpae)
    If you don't immediately see anything, you can always use the quadratic formula

    I'll put it below just for your convenience

    x= \frac{-b \pm \sqrt{b^2-4ac}}{2a}

    By the way, if you're not sure what this is, then you probably haven't done this yet.
    In this case, thomaskurian89's post would probably be more for you :woo:
    Oh yeah. I forgot about that. Thanks for help, i'll try using it now
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    (Original post by Aileena)
    Oh yeah. I forgot about that. Thanks for help, i'll try using it now
    No worries
    Did you get the same answers out?!

    I don't know about you, but I think it's good to have a method that always works, even if there are other "short cut" methods in certain circumstances.
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    All I can do is to say thank you

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    You know who you are! :cute:
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    (Original post by placenta medicae talpae)
    No worries
    Did you get the same answers out?!

    I don't know about you, but I think it's good to have a method that always works, even if there are other "short cut" methods in certain circumstances.
    Yes I did, thank you
 
 
 
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