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nice

  • 5 years ago

how to find the projection of a=(1,3) on b=(4,0,2) ??

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  1. amistre64
    • 5 years ago
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    a onto b eh... vector right? its the |a| cos(angle between)

  2. nice
    • 5 years ago
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    really ? I know diff. formula!!

  3. nice
    • 5 years ago
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    angle is not mentioned at all in the question

  4. amistre64
    • 5 years ago
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    t = \(cos^{-1}(a.b/(|a||b|))\)

  5. amistre64
    • 5 years ago
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    well, in order to know the length of the projection onto b you gotta know the angle between a and b

  6. nice
    • 5 years ago
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    not the length ! it said just the vector that is proj.

  7. amistre64
    • 5 years ago
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  8. amistre64
    • 5 years ago
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    vectors are length and direction...cant have vector without length right?

  9. nice
    • 5 years ago
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    sure! but I'm using the dot product ,, (a.b/||b||^2) x b

  10. amistre64
    • 5 years ago
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    ok...

  11. amistre64
    • 5 years ago
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    <1,3,0> <4,0,2> ------- 4+0+0 =4

  12. nice
    • 5 years ago
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    aha ,, then ?

  13. amistre64
    • 5 years ago
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    sqrt(10).sqt(20) = sqrt(200)

  14. amistre64
    • 5 years ago
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    cos_1(4/sqrt(200)) is what id try

  15. amistre64
    • 5 years ago
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    73.57 degrees is the angle between them...

  16. amistre64
    • 5 years ago
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    but we already have the cos of that: 4/sqrt(200) lol

  17. amistre64
    • 5 years ago
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    4sqrt(10) -------------- = 4/sqrt(20) right? this is the length of a vector sqrt(10).sqrt(20) that is parallel to b

  18. amistre64
    • 5 years ago
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    b/|b| = unit vector of b; then *that to get the vector projection

  19. nice
    • 5 years ago
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    aha that the answer I've found but in diff. way

  20. nice
    • 5 years ago
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    but the problem that it's multiple choice Qs. and I didn't find the answer !!

  21. amistre64
    • 5 years ago
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    <4,0,2> 4 ------- * ----- :) sqrt(20) sqrt20

  22. amistre64
    • 5 years ago
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    whats the choices?

  23. amistre64
    • 5 years ago
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    i get: <16/20 , 0 ,8/20> if im right lol

  24. nice
    • 5 years ago
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    the answers are : <1,1> , <2,1> , <2,-1> , <1,2>

  25. nice
    • 5 years ago
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    that's the answer I've got ! but it seems that its wrong !!!

  26. amistre64
    • 5 years ago
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    well, then we misunderstood what it was asking for then :)

  27. nice
    • 5 years ago
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    the question which is up there is the exact same ques. !!!!!

  28. amistre64
    • 5 years ago
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    yeah, perhaps its the vector that I drew in green?

  29. amistre64
    • 5 years ago
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    http://www.vitutor.com/geometry/vec/vector_projection.html

  30. nice
    • 5 years ago
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    thanks allot for trying ..

  31. amistre64
    • 5 years ago
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    a.b --- * b |b|^2 4/20 = 1/5<4,0,2> = <4/5,0,2/5> cant really see it being nuthin else

  32. amistre64
    • 5 years ago
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    youre welcome :) good luck

  33. nice
    • 5 years ago
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    yes! that's my opinion two !

  34. nice
    • 5 years ago
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    thank you ..

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