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Homework Help: Vectors help please

  1. Mar 2, 2014 #1
    1. The problem statement, all variables and given/known data

    If [itex]\underline{v}[/itex] = a[itex]\underline{i}[/itex] + 2[itex]\underline{j}[/itex] + 3[itex]\underline{k}[/itex] and [itex]\underline{w}[/itex] = 2[itex]\underline{i}[/itex] +b[itex]\underline{j}[/itex] - [itex]\underline{k}[/itex] and |[itex]\underline{v}[/itex]| = |[itex]\underline{w}[/itex]|, find the values of a and b so that [itex]\underline{v}[/itex] and [itex]\underline{w}[/itex] are perpendicular.

    If v = ai+3j+3k and w = 2i+bj-k and |v| = |w|, find the values of a and b so that v and w are perpendicular.

    2. Relevant equations

    [itex]\underline{a}[/itex] - ([itex]\underline{a}[/itex].[itex]\underline{\hat{b}}[/itex])[itex]\underline{\hat{b}}[/itex]

    3. The attempt at a solution
    sqrt(a2+13) = sqrt(b2+5)

    I am so confused right now. Any help would be great. Thanks
  2. jcsd
  3. Mar 2, 2014 #2


    Staff: Mentor

    That's one equation. To get another equation, use the requirement that u and v be perpendicular. Hint: There is a simple operation that can be used to determine whether two vectors are perpendicular.
  4. Mar 2, 2014 #3
    Thanks, haha, so simple. I'm so angry at myself now. :)
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