# Vector trouble

1. Nov 3, 2005

### DB

when a question gives u vectors in polar form, calling them A,B,C,D then askes you to simply for example: A - 4C + D, what am i supposed to do? is it just vector sum and difference? how do i multiply a vector by 4?

thanks

2. Nov 3, 2005

### mathmike

4(xi+yj+zk)=4xi+4yj+4zk

3. Nov 3, 2005

### DB

sry i didnt mention we were working in 2D, but wat are i and j?

4. Nov 3, 2005

### mathmike

i and j is the subscript used to designate the x and y axis

5. Nov 3, 2005

### DB

o i see, sry to be a pain in the butt, but then wat are x and y?

6. Nov 3, 2005

### mathmike

the coefficients of i and j

7. Nov 3, 2005

### Integral

Staff Emeritus
As used above, i and j, represent unit vectors, i in the x direction, j in the y. In 3d you also have k, the unit vector in the z direction.

I would assume that you are taking some form of a math class, have you read your text?

8. Nov 3, 2005

### DB

so 4 * Vector 25, 340 degrees would be 4(23.5+8.6) aproxx??

9. Nov 3, 2005

### DB

physics, my teacher hasnt given us any reading, he just said see if u can get these problems

10. Nov 3, 2005

### DB

is 4(23.5+8.6) right? wat i did was set up the the vector on a cartesian plane and use trig to solve the lenghts, would it be 4(23.5+ -8.6) because the triangle is in the 4th quadrant, or would i take the absolute value?

11. Nov 4, 2005

### finchie_88

If you are trying to work out 4V as a vector, and V is something at 340 degrees, and at a magnitude of 25, then the vector can be written as
$$v = 4(23.5i-8.6j)$$
(approx). The i and j are there to show they are the different components of v.
By the way, I hate this latex thing, I was trying to get the i and j go bold in tex mode, but failed, oh well.