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  1. #1
    Junior Member
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    India
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    Math help.

    If  (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
    Joined
    Aug 2008
    Posts
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    Hello,

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

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

    Bye.
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  3. #3
    Super Member

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    Lexington, MA (USA)
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    Hello, devi!

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


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

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

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

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


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

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