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Math Help - Subtraction of binomial fractions?

  1. #1
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    Subtraction of binomial fractions?

    I'm SO close to getting the answer, but where do I go from here?

    http://oi42.tinypic.com/2505ct3.jpg
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  2. #2
    Senior Member BAdhi's Avatar
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    Re: Subtraction of binomial fractions?

    you cannot take (a^2+b^2)=(a+b)^2 (which you've done in 3rd step) just expand and simplify
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  3. #3
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    Re: Subtraction of binomial fractions?

    Are you sure? Why can't I do that?

    Edit: Either way I get the same answer, which I don't know what to do with..
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  4. #4
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    Re: Subtraction of binomial fractions?

    Remember a^2+b^2 \neq (a+b)^2

    Spoiler:
    \displaystyle x = \sqrt{\frac{10\times 30^2-30\times 10^2}{20}}


    Please avoid attachements if possible
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  5. #5
    Senior Member BAdhi's Avatar
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    Re: Subtraction of binomial fractions?

    because you, yourself has taken (x+30)^2=(x^2+60x+30^2) at one point (on the fifth line)

    so clearly it is not (x^2+30^2)
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  6. #6
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    Re: Subtraction of binomial fractions?

    Quote Originally Posted by pickslides View Post
    Remember a^2+b^2 \neq (a+b)^2

    Spoiler:
    \displaystyle x = \sqrt{\frac{10\times 30^2-30\times 10^2}{20}}


    Please avoid attachements if possible
    Thank you very much, sorry about the attachment!

    So.. How did you just do that?
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  7. #7
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    Re: Subtraction of binomial fractions?

    Quote Originally Posted by AlexWilson94 View Post
    Are you sure? Why can't I do that?
    pick a=2 and b=3, try it for both sides, are they the same?
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  8. #8
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    Re: Subtraction of binomial fractions?

    Quote Originally Posted by BAdhi View Post
    because you, yourself has taken (x+30)^2=(x^2+60x+30^2) at one point (on the fifth line)

    so clearly it is not (x^2+30^2)
    Oohh.. My bad on that.. Sorry, thank you!
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  9. #9
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    Re: Subtraction of binomial fractions?

    Quote Originally Posted by pickslides View Post
    pick a=2 and b=3, try it for both sides, are they the same?
    It clicks now.. Got it, thanks for clearing that up!
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  10. #10
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    Re: Subtraction of binomial fractions?

    Quote Originally Posted by AlexWilson94 View Post

    So.. How did you just do that?
    With pen and paper, you have been told where you went wrong, so have another go at it, post your attempts if you need further clarification.

    You even have the answer now to help you check!
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  11. #11
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    Re: Subtraction of binomial fractions?

    So from the 3rd line, I went:

    (10x^2 + 9000) - (30x^2 + 1000) = 0
    -20x^2 + 6000 = 0
    6000 = -20x^2

    Then I took the square root of both sides, then divided to square root of 6000 by 20, and wualah. x=3.87

    Edit: By the way, how do you get the math symbols?
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  12. #12
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    Re: Subtraction of binomial fractions?

    Quote Originally Posted by AlexWilson94 View Post
    So from the 3rd line, I went:

    (10x^2 + 9000) - (30x^2 + 1000) = 0
    -20x^2 + 6000 = 0
    6000 = -20x^2

    Then I took the square root of both sides, then divided to square root of 6000 by 20, and wualah. x=3.87

    This does not look correct.

    Form your working

    6000 = -20x^2 \implies x= \sqrt{\frac{6000}{-20}}\neq 3.87


    Quote Originally Posted by AlexWilson94 View Post

    Edit: By the way, how do you get the math symbols?
    Put "tex" tags around your equations
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  13. #13
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    Re: Subtraction of binomial fractions?

    [/tex]
    Quote Originally Posted by pickslides View Post
    This does not look correct.

    Form your working

    6000 = -20x^2 \implies x= \sqrt{\frac{6000}{-20}}\neq 3.87




    Put "tex" tags around your equations
    Oh my bad, I forgot to take out the negative when I posted it here.
    It's supposed to be 20x^2, since I added it to both sides. Thanks!
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