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  1. #1
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    Question Expand

    Hi

    What do i get when i expand:

    x^2 - 1

    Is it
    (x-1)(x+1)
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by taurus View Post
    Hi

    What do i get when i expand:

    x^2 - 1
    expand? there is nothing to expand here, you'd get just that. did you mean factorize? this is the difference of two squares, x^2 - 1 = (x + 1)(x - 1)
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  3. #3
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    yes thanks
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  4. #4
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    Just a quick question:
    is it ok to write

    21 - 4x - x^2

    as

    x^2 + 4x - 21?
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  5. #5
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by taurus View Post
    Just a quick question:
    is it ok to write

    21 - 4x - x^2

    as

    x^2 + 4x - 21?
    not unless it is equated to something where you can distribute the minus on the other side as well:

    so, say you had: 21 - 4x - x^2 = 0

    then it is okay to multiply both sides by -1 to get: x^2 + 4x - 21 = 0


    but if you just have the expression by itself, you cannot do that, the best you can do is to say:

    21 - 4x - x^2 = - \left( x^2 + 4x - 21 \right)

    leave the minus outside of the brackets
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  6. #6
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    Question

    so for example this:

    1/(21-4x-x&2)

    Which one do i use?
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  7. #7
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by taurus View Post
    so for example this:

    1/(21-4x-x&2)

    Which one do i use?
    it is not equated to anything.

    \frac 1{21 - 4x - x^2} = \frac {-1}{x^2 + 4x - 21}
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