Thread: Vector problems

I just started on vector and there are some confusing problems i want to ask:

Find the magnitude and direction angle of the vector:
1)$\displaystyle 3i-4j$<- on this one i found the magnitude but not the direction angle, though i'm positive that i did just like i've done with some previous problems. I got 53.13, but the answer in the book is 306.87

2)$\displaystyle -3i-5j$<-- i also got the magnitude of this one, but not the direction angle. again

3)$\displaystyle 7(cos135i+sin135j)$

Find the vector v with the given magnitude and the same direction as u
$\displaystyle |v| = 1, u =<3,-3>$
Please help! Thanks

Originally Posted by nhunhu9

I just started on vector and there are some confusing problems i want to ask:

Find the magnitude and direction angle of the vector:
1)$\displaystyle 3i-4j$<- on this one i found the magnitude but not the direction angle, though i'm positive that i did just like i've done with some previous problems. I got 53.13, but the answer in the book is 306.87

+i , -j ... quadrant IV angle

2)$\displaystyle -3i-5j$<-- i also got the magnitude of this one, but not the direction angle. again

-i , -j ... quadrant III angle

3)$\displaystyle 7(cos135i+sin135j)$

what is your problem with this vector?

Find the vector v with the given magnitude and the same direction as u
$\displaystyle |v| = 1, u =<3,-3>$

v = < 1/sqrt(2) , -1/sqrt(2) >

...

Number 3 is also find the direction angle but since the fisrt and second problems have to do with quadrant i already firgured it out. Thank you