Results 1 to 5 of 5

Math Help - help..

  1. #1
    Junior Member
    Joined
    Oct 2008
    Posts
    42

    help..

    Find the vector u=(abc) such that:
    (i) u is perpendicular to both the vectors (-1,-1,-2) and (9,-9,0)

    (ii) u= (27)^{1/2}

    (iii) a0

    thanks in advance for any help..
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by omibayne View Post
    Find the vector u=(abc) such that:
    (i) u is perpendicular to both the vectors (-1,-1,-2) and (9,-9,0)

    (ii) u= (27)^{1/2}

    (iii) a0

    thanks in advance for any help..
    (i) Take the cross product of (-1, -1, -2) and (9, -9, 0).

    (ii) Find the unit in the direction of u and multiply it by (27)^{1/2}.

    (iii) Multiply u by -1 if it turns out that a < 0 in the above calculations.
    Last edited by mr fantastic; November 8th 2008 at 09:16 PM. Reason: Got rid of a redundant =
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Oct 2008
    Posts
    42
    Quote Originally Posted by mr fantastic View Post
    (i) Take the cross product of (-1, -1, -2) and (9, -9, 0).

    (ii) Find the unit in the direction of u and multiply it by = (27)^{1/2}.

    (iii) Multiply u by -1 if it turns out that a < 0 in the above calculations.

    ok so i got (-18,-18,18) for the cross product....i still cannot figure out part (ii)...can u explain it a little bit more..i will appreciate that alot..thanks
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by omibayne View Post
    ok so i got (-18,-18,18) for the cross product....i still cannot figure out part (ii)...can u explain it a little bit more..i will appreciate that alot..thanks
    Do you know how to find the magnitude of a vector? Do you know how to divide a vector by a scalar. If your answer to both these questions is yes, then you know how to get a unit vector.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Oct 2008
    Posts
    42
    Quote Originally Posted by mr fantastic View Post
    Do you know how to find the magnitude of a vector? Do you know how to divide a vector by a scalar. If your answer to both these questions is yes, then you know how to get a unit vector.
    yes i do know and i got the answer..thanks again for ur help
    Follow Math Help Forum on Facebook and Google+


/mathhelpforum @mathhelpforum