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Math Help - equation

  1. #1
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    equation

    Hi,

    I have an exam in the next couple of days that I am really not looking forward to.

    Can anyone explain to me how the 6.8CR is derived in the following sum?
    I see how we get to 13, but 6.8CR is a mystery to me.



    Thanks,
    TK
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  2. #2
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    Quote Originally Posted by tomjkear View Post
    Hi,

    I have an exam in the next couple of days that I am really not looking forward to.

    Can anyone explain to me how the 6.8CR is derived in the following sum?
    I see how we get to 13, but 6.8CR is a mystery to me.



    Thanks,
    TK
    Expand the brackets (I'm goin to use x = C_R. It's easier to type:

    (2 - 0.8x)^2+(-3+0.6x)^2=4-3.2x+0.64x^2 + 9 - 3.6x + 0.36x^2

    Collect like terms and you'll get the given result.

    Probably you missed that

    (2-0.8x)^2 = (2-0.8x)(2-0.8x)
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  3. #3
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    Quote Originally Posted by earboth View Post
    Expand the brackets (I'm goin to use x = C_R. It's easier to type:

    (2 - 0.8x)^2+(-3+0.6x)^2=4-3.2x+0.64x^2 + 9 - 3.6x + 0.36x^2

    Collect like terms and you'll get the given result.

    Probably you missed that

    (2-0.8x)^2 = (2-0.8x)(2-0.8x)
    Thanks, but I still don't understand
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by tomjkear View Post
    Thanks, but I still don't understand
    FOIL it out. For example:
    (2 - 0.8x)^2 = (2 - 0.8x)(2 - 0.8x) = 2 \cdot 2 + 2 \cdot -0.8x + -0.8x \cdot 2 + -0.8x \cdot -0.8x

    = 4 - 1.6x - 1.6x + 0.64x^2 = 4 - 3.2x + 0.64x^2

    Try that on your other term.

    -Dan
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  5. #5
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    Quote Originally Posted by tomjkear View Post
    Thanks, but I still don't understand
    I would like to help you but you have to describe exactly what you didn't understand.
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  6. #6
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    Quote Originally Posted by earboth View Post
    Expand the brackets (I'm goin to use x = C_R. It's easier to type:

    (2 - 0.8x)^2+(-3+0.6x)^2=4-3.2x+0.64x^2 + 9 - 3.6x + 0.36x^2

    Collect like terms and you'll get the given result.

    Probably you missed that

    (2-0.8x)^2 = (2-0.8x)(2-0.8x)
    Quote Originally Posted by earboth View Post
    I would like to help you but you have to describe exactly what you didn't understand.
    It's OK, both your post and the post from the person above have clarified, thanks very much
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