Simple Calc

[MSCALC]

Hi Members,

I was hoping a smart someone may be able to get rid of my confusion regarding this question.

Question: Vectors a and b are unit vectors between a and b is 30 deg. Calculate 3a-2b.

My Calculation: For magnitude I simply used the cos law (a^2= B^c+c^2-2(b)(c)CosA). That part was simple and I got my answer of 1.62. Then I calculated the direction of the resultant vector but I am not getting the same answer as I should get which is "bearing 131 deg". I used the sin law and got 68 deg for the angle of the resultant vector. Can someone show me how to get bearing 131.


Thanks, all efforts are much appreciated.

 

[HallsofIvy]

If all you have "Vectors a and b are unit vectors between a and b is 30 deg" You cannot say anything about the "bearing". All you can say is that 3a-2b makes a certain angle with vector a (or with vector b). I get that 3a- 2b is 158 degrees from vector b and 129 degrees from vector b.

 

[MSCALC]

Thanks for your answer.

That is what is confusing me too, how can I caculate a bearing given two unit vectors with a 30 deg angle in between. I'm guessing I can calculate the bearing in relation with each other but not a true bearing.