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    Hi so the simultaneous equations are x^2-2xy-y^2=7
    x+y=1
    I rearranged x+y=1 to get x=1-y
    I substituted into the first equation
    which i got (1-y)^2 -2y(1-y)-y^2=7
    after expanding the brackets and simplifying i got -6-3y+y^2=0
    I feel like i have done something wrong as it cant be factorised and I went onto desmos and putting this into a quadratic equation gives me wrong solutions. Have I went wrong expannding brackets?
    need help thank you.
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    (Original post by 5h3bi)
    Hi so the simultaneous equations are x^2-2xy-y^2=7
    x+y=1
    I rearranged x+y=1 to get x=1-y
    I substituted into the first equation
    which i got (1-y)^2 -2y(1-y)-y^2=7
    after expanding the brackets and simplifying i got -6-3y+y^2=0
    I feel like i have done something wrong as it cant be factorised and I went onto desmos and putting this into a quadratic equation gives me wrong solutions. Have I went wrong expannding brackets?
    need help thank you.
    Yeah you expanded wrong, try expanding again more carefully. Post a picture of your working out of the expansion if it still doesn't work.
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    (Original post by Zacken)
    Yeah you expanded wrong, try expanding again more carefully. Post a picture of your working out of the expansion if it still doesn't work.
    Now i seem to be getting -6+y+y^2=0
    seems to still be wrong
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    (Original post by 5h3bi)
    Now i seem to be getting y^2+y-6=0
    seems to still be wrong
    Like I said, post a picture of your working out for the expansion or type it up.
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    (Original post by Zacken)
    Like I said, post a picture of your working out for the expansion or type it up.
    (1-y)^2-2y(1-y)-y^2=7
    (1-y) (1-y) when i expand this i get 1-y-y+y as 1*1 is 1, 1* -y is -y and -y again and -y*-y is +y
    and when i expand 2y(1-y)
    i get 2y-2y^2
    so this gives me
    1-y-y+y - 2y-2y^2-y^2=7
    collecting like terms I get y-2y-y^2=7
    subtracting 7 to get
    y-2y-y^2-7=0
    i keep expanding and getting different answers?
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    (Original post by 5h3bi)
    (1-y)^2-2y(1-y)-y^2=7
    (1-y) (1-y) when i expand this i get 1-y-y+y as 1*1 is 1, 1* -y is -y and -y again and -y*-y is +y

    No. (-y)(-y)=y^2 \not= y


    (Original post by 5h3bi)
    .. - 2y-2y^2-y^2=7
    Also no. -2xy=-(2y-2y^2)
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    (Original post by 5h3bi)
    (1-y)^2-2y(1-y)-y^2=7
    (1-y) (1-y) when i expand this i get 1-y-y+y as 1*1 is 1, 1* -y is -y and -y again and -y*-y is +y
    This bit is wrong, you get: (1-y)(1-y) = 1(1-y) - y(1-y) = 1 - y - y + y^2 = 1- 2y + y^2
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    (Original post by leadheadsmith)
    [...]
    No full solutions.
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    (Original post by Zacken)
    This bit is wrong, you get: (1-y)(1-y) = 1(1-y) - y(1-y) = 1 - y - y + y^2 = 1- 2y + y^2
    thanks it was due to my careless expanding of brackets, however I will now know for future lessons to carefully expand brackets. Thanks alot for helping Zacken and RDK games.
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    (Original post by 5h3bi)
    thanks it was due to my careless expanding of brackets, however I will now know for future lessons to carefully expand brackets. Thanks alot for helping Zacken and RDK games.
    You're welcome!
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    (Original post by Zacken;[url="tel:67647586")
    67647586[/url]]No full solutions.
    Haven't done simultaneous equations in ages haha
 
 
 
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