Surds

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  1. bahjat93's Avatar
    1 08-05-2012  19:39
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    Surds
    can some1 please explain to me how you would solve
    sqrt45 + 20/sqrt5

    Sqrt=square root
  2. raheem94's Avatar
    2 08-05-2012  19:44
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    Re: Surds
    (Original post by bahjat93)
    can some1 please explain to me how you would solve
    sqrt45 + 20/sqrt5

    Sqrt=square root
    \displaystyle \sqrt{45} + \frac{20}{\sqrt5}

    Remember, \displaystyle \sqrt{45} = \sqrt{9 \times 5 } = \sqrt9 \times \sqrt5
  3. bahjat93's Avatar
    3 08-05-2012  19:46
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    Re: Surds
    (Original post by raheem94)
    \displaystyle \sqrt{45} + \frac{20}{\sqrt5}

    Remember, \displaystyle \sqrt{45} = \sqrt{9 \times 5 } = \sqrt9 \times \sqrt5
    i got that far but i couldn't go any further then that .
    This is the only question i'm stuck on in the ENTIRE exam paper
  4. Booyah's Avatar
    4 08-05-2012  19:49
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    Re: Surds
    I would rationalise the denominator... If that makes sense...
  5. raheem94's Avatar
    5 08-05-2012  19:50
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    Re: Surds
    (Original post by bahjat93)
    i got that far but i couldn't go any further then that .
    This is the only question i'm stuck on in the ENTIRE exam paper
    \displaystyle \sqrt{45} + \frac{20}{\sqrt5}

    \sqrt{45} = \sqrt9 \times \sqrt5 = 3 \sqrt5

    \displaystyle \sqrt{45} + \frac{20}{\sqrt5} = 3 \sqrt5 + \frac{20}{\sqrt5} = \frac{3 \sqrt5 \ \sqrt5}{\sqrt5} + \frac{20}{\sqrt5}

    Can you now do it?
    Last edited by raheem94; 08-05-2012 at 19:51.
  6. bahjat93's Avatar
    6 08-05-2012  19:50
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    Re: Surds
    (Original post by Booyah)
    I would rationalise the denominator... If that makes sense...
    Could you turn your statement into numbers please
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  7. Rainingshame's Avatar
    7 08-05-2012  19:53
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    Re: Surds
    do the cross and smile technique. sqrt45 = sqrt45/1
    Multiply the denominators together. Multiply each numerator with the opposite denominator. Add them together. So (sqrt45*sqrt5 + 20)/sqrt5
    (sqrt9*sqrt5*sqrt5 +20)/sqrt5
    =(3*5+20)/sqrt5
    =(15+20)/sqrt5
    =35/sqrt5
  8. Booyah's Avatar
    8 08-05-2012  20:00
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    Re: Surds
    (Original post by bahjat93)
    Could you turn your statement into numbers please


    So you would multiply 20/5^1/2 by( 5^1/2 ) / ( 5^1/2 )
  9. bahjat93's Avatar
    9 08-05-2012  20:04
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    Re: Surds
    (Original post by Rainingshame)
    do the cross and smile technique. sqrt45 = sqrt45/1
    Multiply the denominators together. Multiply each numerator with the opposite denominator. Add them together. So (sqrt45*sqrt5 + 20)/sqrt5
    (sqrt9*sqrt5*sqrt5 +20)/sqrt5
    =(3*5+20)/sqrt5
    =(15+20)/sqrt5
    =35/sqrt5
    That's very helpful m8, ty.
    another question, how would you turn
    35/sqrt5 into 7sqrt5 ???
  10. nuodai's Avatar
    10 08-05-2012  20:06
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    Re: Surds
    (Original post by bahjat93)
    That's very helpful m8, ty.
    another question, how would you turn
    35/sqrt5 into 7sqrt5 ???
    Multiply the numerator and denominator by \sqrt{5} and see what cancels.
  11. bahjat93's Avatar
    11 08-05-2012  20:09
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    Re: Surds
    (Original post by nuodai)
    Multiply the numerator and denominator by \sqrt{5} and see what cancels.
    Ty, i just realised i was being an idiot :/, i thought multiplying the denominator and the numerator by sqrt 5 would cancel the sqrt 5 at the bottom but i see the error of my ways now.

    Ty every1 who answered/attempted to answer my question, much appreciated.
    Good luck on your exam guys
  12. jadomcp's Avatar
    12 08-05-2012  20:12
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    Re: Surds
    sqrt45 = 3sqrt5
    therefore, sqrt45+20sqrt5 = 3sqrt5+20sqrt5 = 23sqrt5
    so your answer is 23sqrt5
  13. GreenLantern1's Avatar
    13 08-05-2012  20:14
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    Re: Surds
    (Original post by jadomcp)
    sqrt45 = 3sqrt5
    therefore, sqrt45+20sqrt5 = 3sqrt5+20sqrt5 = 23sqrt5
    so your answer is 23sqrt5
    Number 1: Don't post full solutions
    Number 2: That solution is wrong. It is (20sqrt5)/5 = 4 sqrt5
  14. zed963's Avatar
    14 08-05-2012  20:33
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    Re: Surds
    (Original post by raheem94)
    \displaystyle \sqrt{45} + \frac{20}{\sqrt5}

    \sqrt{45} = \sqrt9 \times \sqrt5 = 3 \sqrt5

    \displaystyle \sqrt{45} + \frac{20}{\sqrt5} = 3 \sqrt5 + \frac{20}{\sqrt5} = \frac{3 \sqrt5 \ \sqrt5}{\sqrt5} + \frac{20}{\sqrt5}

    Can you now do it?
    can you show me the full working out to this question
  15. raheem94's Avatar
    15 08-05-2012  20:37
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    Re: Surds
    (Original post by zed963)
    can you show me the full working out to this question
    \displaystyle \frac{3 \sqrt5 \ \sqrt5}{\sqrt5} + \frac{20}{\sqrt5} = \frac{3 \times 5}{\sqrt5} + \frac{20}{\sqrt5} = \frac{15}{\sqrt5}+ \frac{20}{\sqrt5}= \frac{15+20}{\sqrt5}= \frac{35}{\sqrt5} = \frac{35\sqrt5}{\sqrt5 \times \sqrt5} = \frac{35\sqrt5}{5} = 7\sqrt5

    Done.

    Do you understand it?
  16. zed963's Avatar
    16 08-05-2012  20:40
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    Re: Surds
    (Original post by raheem94)
    \displaystyle \frac{3 \sqrt5 \ \sqrt5}{\sqrt5} + \frac{20}{\sqrt5} = \frac{3 \times 5}{\sqrt5} + \frac{20}{\sqrt5} = \frac{15}{\sqrt5}+ \frac{20}{\sqrt5}= \frac{15+20}{\sqrt5}= \frac{35}{\sqrt5} = \frac{35\sqrt5}{\sqrt5 \times \sqrt5} = \frac{35\sqrt5}{5} = 7\sqrt5

    Done.

    Do you understand it?
    Not exactly were have u got 3root5 root 5 from
  17. steve2005's Avatar
    17 08-05-2012  20:43
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    • Location: LONDON
    Re: Surds
    (Original post by raheem94)
    \displaystyle \frac{3 \sqrt5 \ \sqrt5}{\sqrt5} + \frac{20}{\sqrt5} = \frac{3 \times 5}{\sqrt5} + \frac{20}{\sqrt5} = \frac{15}{\sqrt5}+ \frac{20}{\sqrt5}= \frac{15+20}{\sqrt5}= \frac{35}{\sqrt5} = \frac{35\sqrt5}{\sqrt5 \times \sqrt5} = \frac{35\sqrt5}{5} = 7\sqrt5

    Done.

    Do you understand it?
    This is what I would do.
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  18. zed963's Avatar
    18 08-05-2012  20:45
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    Re: Surds
    (Original post by steve2005)
    This is what I would do.
    Good explanation.

    Can you give me a question like that.
  19. raheem94's Avatar
    19 08-05-2012  20:47
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    Re: Surds
    (Original post by steve2005)
    This is what I would do.
    Your way is better.
  20. zed963's Avatar
    20 08-05-2012  20:55
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    Re: Surds
    (Original post by raheem94)
    Your way is better.
    Can u give me a question like that
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