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At school a few of our classes this semester have begun using vectors in the form of r<θ to solve problems but I never learn this method of solving problems and I would really appriciate it if you guys would help me out with this! (:

I know that r<θ = r cosθ i + r sin j but what happens when you have a 3D based coordinate (i.e. vecotrs with i, j and k components)?

Also, I know that when you dot two vectors in the form of r<θ together, you get (r + r) cos (θ+θ) similarly when you cross you get (r + r) sin (θ+θ) right?

Now when you cross the vectors, how do you know what component you end up with? I know that if you cross 3i + 2j with 6i + 2j you end up with a vector with only a k component but how do you see this? How if I have like 4k x r<θ how do I solve it then?

I know it'a mouthful but I'm really hoping that someone can guide me on this or if possible direct me to a site or (preferbly) a youtube video that teaches this. I haven't been able to find anything at all. ):

Thanks guys!

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# Homework Help: Vectors in the form r<θ

**Physics Forums | Science Articles, Homework Help, Discussion**