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Thread: Math help.

  1. #1
    Junior Member
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    India
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    Math help.

    If $\displaystyle (x-1/x) = 5 the value of x^2+1/x is $
    (a)23
    (b)27
    (c)25
    (d)29
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  2. #2
    Member
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    Hello,

    I think something is wrong...
    If you are asked the value of $\displaystyle x^2+\frac{1}{x^2}$, compute $\displaystyle \left(x-\frac{1}{x}\right)^2$ and compare.

    If you really want $\displaystyle x^2+\frac{1}{x}$, the easiest way may be to compute the value of x by $\displaystyle x^2-1=5x$.

    Bye.
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  3. #3
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    Hello, devi!

    You really should learn to control the text when using LaTeX.
    $\displaystyle Otherwise everything looks like this.$


    If $\displaystyle x-\frac{1}{x} \:=\:5$, the value of $\displaystyle x^2+\frac{1}{x^2}$ is:

    . . $\displaystyle (a)\;23 \qquad(b)\;27 \qquad (c)\;25 \qquad(d)\;29$

    We are given: .$\displaystyle x - \frac{1}{x} \:=\:5$

    Square both sides: .$\displaystyle \left(x-\frac{1}{x}\right)^2 \:=\:5^2 \quad\Rightarrow\quad x^2 - 2 + \frac{1}{x^2} \;=\;25$


    Therefore: .$\displaystyle x^2 + \frac{1}{x^2} \;=\;27\;\;(b)$

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