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i think it is 0+2kpi

thats no possiable as one of the given solutions..

theres a relationship between cos and dot products, do you recall it?

yes.

then the angle is simple to be found knowing:\[|u||v|cos~\alpha=u \cdot v\]

solve for alpha :)

i remember the formula how do i plug the numbers into the formula?

you know how to do a dot product right? and to find lengths of vectors?

yeah

those are the numbers you need then, what do you get for:
u.v
and the lengths of u and v ?

38

the 38 came from 42+(-4)

lol ... i do tend to add when i need to multiply when doing that

-1*-4 is +4, and i did a +5 :)

okay thank you i got 20.28?

i got something closer to 10

http://www.wolframalpha.com/input/?i=arccos%2848%2Fsqrt%2837*65%29%29