# Vector help asap

1. Jan 12, 2005

### HawKMX2004

vector help asap plz!!

I have a problem that says define the i,j form of a vector and write the following vectors in i,j form u = P(1,1) to Q(2,4) and v = P(6, -3) to Q(7,0). I looked all through my book, and cannot find a definition for the i,j form of a vector ( i checked glossary, index,l and read the whole chapter again) I'm sure if i had a definition I could figure out how to re write the vectors...can anyone help please?

2. Jan 12, 2005

### dextercioby

I don't know whether anyone can help,but hopefully i can.A vector in i+j form is expressed starting with its form in a basis.
Exempli gratia:
The vector $\vec{A}$ in the base $\vec{i},\vec{j}$has the form:
$$\vec{A}=5\vec{i}+7\vec{j} [/itex] ,so i step in and define its "i+j form" by the ordered pair: [tex] \vec{A}(\vec{i},\vec{j})=:(5,7)$$

Using this simple example,try to solve your problem.

Daniel.

Last edited: Jan 12, 2005
3. Jan 12, 2005

### HawKMX2004

ok so for U for example, U in form i,j would be 1i + 1j and 2i + 4j ?? im lost a little or does this mean 2i + 1i = 3 and 4j + 1j = 5 so U(i,j) = (3,5) ??

4. Jan 13, 2005

### HallsofIvy

Staff Emeritus
Do you have no idea at all what a vector is?

u is a vector from (1,1) to (2,4): The x component changes from 1 to 2 so it changes by 2-1= 1. The y component changes from 1 to 4 so it changes by 4-1= 3.
The "i" number is the x change and the "j" number is the y change:
u= 1i+ 3j (and that is NOT 4 anything!)

v runs from (6, -3) to (7,0). The x component changes from 6 to 7: it changes by 1. The y component changes from -3 to 0: it changes by 0-(-3)= 3.
v= 1i+ 3j (it's the same as u!)