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Perpendicular unit vector

  • Thread starter TW Cantor
  • Start date
  • #1
54
1

Homework Statement



Given that a = (-1,16,-1) and b = (-18,-15,-15),


find the unit vector which is perpendicular to the plane containing a and b.

There are two possible answers. Choose the answer with a positive x component.


Homework Equations



(a*b) = (a2*b3-a3*b2)i - (a1*b3-a3*b1)j - (a1*b2-a2*b1)k

(a*b)/(|a*b|) = unit vector

The Attempt at a Solution



using the above formula i worked out (a*b)= -255i + 3j - 303K

the modulus of a*b is therefore: sqrt(2552 + 32 + 3032)

i then put these values into the equation and i get:

-0.6438i + 0.008j - 0.7651k

since i need to make it positive in the x component my final answer is:

0.644i + 0.008 - 0.765k

am i doing this correctly? it just seems like a very unusual numbers
 

Answers and Replies

  • #2
1,137
0
well if there is a vector A then vector opposite to A is -A ... changing only x component makes it something different
 
  • #3
1,137
0
you can always check if its a unit vector or not,its magnitude should be 1

as this one's mag in approx 1.01 .. i guess your answer is correct
 

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