1
$\begingroup$

The vectors a and b are unit vectors that make an angle of 60 degrees with each other. If a-3b and ma+3b are perpendicular, determine the value of m. I'm lost and am not sure on how to begin solving this question.

$\endgroup$
  • 1
    $\begingroup$ Try computing the dot product $$(a - 3b) \cdot (ma + 3b)$$. $\endgroup$ – user61527 May 22 '14 at 2:45
  • $\begingroup$ I did and I got: ma^2 - ab + 3mab - 3b^2. I am not sure what follows this though $\endgroup$ – user481710 May 22 '14 at 2:49
0
$\begingroup$

$\left \langle a,b \right \rangle$ = $\left \| a \right \|$.$\left \| b \right \|$.cos(60) but a and b are unit vectors so $\left \langle a,b \right \rangle$ = cos(60). $\left \langle a-3b,ma+3b \right \rangle$ = 0 because cos(90) = 0. You should be able to conclude the rest.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.