# Vector problems

• Jul 19th 2010, 10:35 AM
nhunhu9
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>\$
• Jul 19th 2010, 01:56 PM
skeeter
Quote:

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) >

...
• Jul 19th 2010, 04:27 PM
nhunhu9
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