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Ok, here is my problem. I haven't taken anything vector related since at least one year ago. And back then, I wasn't such a good student.. So now my past has come back to haunt me..

I still have some basic notions, but other than that, I pretty much forgot things..

http://img393.imageshack.us/img393/8378/mec1wi0.jpg [Broken]

Can someone please explain to me why i

Why isn't for example i

Our teacher told us that these two are formulas. Or do they vary in each case?

(i

Thanks in advance for your help.

I still have some basic notions, but other than that, I pretty much forgot things..

http://img393.imageshack.us/img393/8378/mec1wi0.jpg [Broken]

Can someone please explain to me why i

_{r}= cosθ . i + sinθ . j and iθ = -sinθ.i + cosθ. j ?Why isn't for example i

_{θ}= -cosθ.i + sinθ.j?Our teacher told us that these two are formulas. Or do they vary in each case?

(i

_{r}, i_{θ}, i and j are vectors.)Thanks in advance for your help.

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