Is this the right way to solve this problem?

  • Thread starter Math9999
  • Start date
  • #1
Math9999

Homework Statement


Determine whether the angle between u=[2, 1] and v=[1, -3] is acute, obtuse, or a right angle.

Homework Equations


None.

The Attempt at a Solution


a*b=2*1+1(-3)=2+(-3)=-1, since the answer is negative, it means the angle is obtuse, am I right? Or is this even the right way of doing this problem? If not, then please correct me.
 

Answers and Replies

  • #2
andrewkirk
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That's correct.
Another way to do it is to swap the x and y coordinates of one vector and make one of them negative. That gives you a vector at right angles to the original. Drawing that new vector and comparing it to the second vector will make it easy to see whether the angle between u and v is acute, right or obtuse.
 
  • #3
Math9999
So the answer is obtuse?
 

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