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Math Help - Ratios/equations

  1. #1
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    Ratios/equations

    If a:b=3:5, find the value of \dfrac{a}{\sqrt{b^2-a^2}}
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by requal View Post
    If a:b=3:5, find the value of \dfrac{a}{\sqrt{b^2-a^2}}
    note that we have \frac ab = \frac 35, that is, a = \frac 35b

    replace a with this expression in \frac a{\sqrt{b^2 - a^2}} and simplify
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  3. #3
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    i dont think that works as (3/5b)^2 is larger than b^2 thus creating a negative number under a square root?
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by requal View Post
    i dont think that works as (3/5b)^2 is larger than b^2 thus creating a negative number under a square root?
    1 - 9/25 is positive. so you have 1b^2 - (9/25)b^2 = (16/25)b^2. how is this negative?
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  5. #5
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    yep, sorry I had mental diaharea thanks anyway
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