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Math Help - solve: lx-3l - lx-1l << 2

  1. #1
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    solve: lx-3l - lx-1l << 2

    solve: lx-3l - lx-1l << 2

    I got x<<1 but i think its wrong.

    THank u
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  2. #2
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    Quote Originally Posted by differentiate View Post
    solve: lx-3l - lx-1l << 2

    I got x<<1 but i think its wrong. .......True!

    THank u
    1. Use the definition of the absolute value:

    |x-3| = \left\{\begin{array}{lcr}x-3&if&x \geq 3\\-(x-3)&if&x < 3\end{array}\right.

    |x-1| = \left\{\begin{array}{lcr}x-1&if&x \geq 1\\-(x-1)&if&x < 1\end{array}\right.

    2. Thus you get three different intervals. Now re-write the equation without absolute values:

    x < 1~:~\begin{aligned}-(x-3)-(-(x-1)) \leq 2\\-x+3+x-1\leq2\\2\leq2\end{aligned}

    1\leq x<3~:~\begin{aligned}-(x-3)-(x-1) \leq 2\\ -2x\leq 2\\x \geq 1\end{aligned}

    x \geq 3~:~\begin{aligned}(x-3)-(x-1) \leq 2\\-3+1\leq2\\-2\leq2\end{aligned}

    Therefore the solution is: x \in \mathbb{R}
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  3. #3
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    Quote Originally Posted by earboth View Post
    1. Use the definition of the absolute value:

    |x-3| = \left\{\begin{array}{lcr}x-3&if&x \geq 3\\-(x-3)&if&x < 3\end{array}\right.

    |x-1| = \left\{\begin{array}{lcr}x-1&if&x \geq 1\\-(x-1)&if&x < 1\end{array}\right.

    2. Thus you get three different intervals. Now re-write the equation without absolute values:

    x < 1~:~\begin{aligned}-(x-3)-(-(x-1)) \leq 2\\-x+3+x-1\leq2\\2\leq2\end{aligned}

    1\leq x<3~:~\begin{aligned}-(x-3)-(x-1) \leq 2\\ -2x\leq 2\\x \geq 1\end{aligned}

    x \geq 3~:~\begin{aligned}(x-3)-(x-1) \leq 2\\-3+1\leq2\\-2\leq2\end{aligned}

    Therefore the solution is: x \in \mathbb{R}
    oh no, that was the solution I wrote on my exam paper but then I changed it into x<<1!!!! OMG!!!!!!!!! I still had all real x values in pencil, but I don't think they will give me the mark ARGH!! THank you. I can't believe I got the answer and then rubbed it out. I am so stupid!
    Last edited by mr fantastic; March 12th 2009 at 03:50 AM. Reason: gd --> n
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