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Maths P3 !!!Need help in finding perpendicular distance between point and line!!!

Discussion in 'International A And AS Level' started by Mayukh, Oct 11, 2015.

  1. Mayukh

    Mayukh

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    Can someone please help me with vectors. For some reason, whenever I do any of the maths involving finding the distance between a point and a line, the answers never match. Can someone give me a tip on how to solve this type of problems.

    When I solve it I find the unit vector in the direction of the line. Let's call it u. I also find the vector of a line from a part of r=a+tb. Let's call it c.

    I find c.u, |c| and take the shortest distance as sqrt{(c.u)^2+(|c|)^2}

    Could somebody please tell me what I'm doing wrong?
    Thanks
     
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  3. Serial_Ripper

    Serial_Ripper

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    Um...I'm not that good at vectors either, but the answers usually match......I can explain in if you give me one of the questions which are bothering you.
     
  4. Mayukh

    Mayukh

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    One of the questions is q2 from the p3 book.

    find the distance of (1,0,0) from r=t(12i-3j-4k)

    my soln:
    a=i
    unit vector in direction r, n=(12/13)i-(3/13)j-(4/13)k
    a.n=12/13
    |a|=1
    so, shortest distance=sqrt(1-(12/13)^2)=5/13

    answer on the back of the book is (1/13)*sqrt(69)
     
  5. Serial_Ripper

    Serial_Ripper

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    SORRY FOR BEING LATE!!
    I THINK IT'S BETTER IF YOU USE EXAMPLES FROM PAST PAPERS...
    I took screenshots of the way I solve this type of question but i've got no idea how to post the photo...PLZ TELL ME HOW!
    DON'T WORRY! THE MAIN PROB WITH THIS QUESTION IS CONCENTRATION !
     
  6. nehaoscar

    nehaoscar

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    Just copy the screenshot and paste it here
     
  7. Serial_Ripper

    Serial_Ripper

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    Not working
     
  8. nehaoscar

    nehaoscar

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    Try using the snipping tool if you have in the computer ... that works for me when i paste it :)
     
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  9. Serial_Ripper

    Serial_Ripper

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  10. Serial_Ripper

    Serial_Ripper

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    hope you'll find them useful!
     
  11. Serial_Ripper

    Serial_Ripper

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    THNX!
     
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  12. Mayukh

    Mayukh

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    Thanks for the reply and I'm sorry for not replying myself.

    If you're giving the exam on Thursday, good luck. Pray for me too 'cause I'm givin the exam too.
     

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