Find the direction angle of v for the following vector.

v = -7i - 9j

Ok, since we can write this as (-7,-9) and this is a triangle we can use
tan a = -9/-7
tan a = 9/7

Ok I need to solve. How do I do that. What I keep coming up with is wrong. Do I just user the $ tan^{-1}(9/7) $

Question

Find the direction angle of v for the following vector.

v = -7i - 9j

Ok, since we can write this as  (-7,-9) and this is a triangle we can use
 tan a = -9/-7 
 tan a = 9/7

Ok I need to solve. How do I do that. What I keep coming up with is wrong. Do I just user the $ tan^{-1}(9/7) $

anonymous · Answer

I need it in degrees

anonymous · Answer

$ tan^{-1}(9/7) $  is suppose to be $ \huge tan^{-1} (\frac{9}{7}) $

anonymous · Answer

and once I find that subtract 360?

anonymous · Answer

@peachpi

anonymous · Answer

@math1234

anonymous · Answer

Are you getting 52.1°?

anonymous · Answer

Yes,  52.125

anonymous · Answer

Then I subtract that by 360, which gives 307.87

anonymous · Answer

But this is wrong.

anonymous · Answer

I think it has something to do with the quadrant it is in.

anonymous · Answer

52.125 is the angle in the 1st quadrant. (-7, -9) is in the 3rd quadrant. You need to add 180.

anonymous · Answer

Ah that is it. I knew it had to do with the quadrant lol

anonymous · Answer

Yep that was it. I was working with it as in the 4th quadrant.

anonymous · Answer

ah ok. it's hard to keep those straight