1. ## Vectors

The line passes through points (0,.5,1) and (2,1,-3) find parametric equations and symmetric equations for the line

I went ahead and subtracted (2,1,-3) from (0,.5,1) and ended up getting right answer, later to find out i subtract other way around to get right answer. Since its matters what which one subtracts from which one how do i determine which one to subtract from, the one with a higher z value? sorry the teacher never told me

2. Originally Posted by usvn
The line passes through points (0,.5,1) and (2,1,-3) find parametric equations and symmetric equations for the line

I went ahead and subtracted (2,1,-3) from (0,.5,1) and ended up getting right answer, later to find out i subtract other way around to get right answer. Since its matters what which one subtracts from which one how do i determine which one to subtract from, the one with a higher z value? sorry the teacher never told me
as far as finding the equation of a line goes, it does not matter. the vectors you get will be parallel, just pointing in opposite directions, and so, either vector can be used as a direction vector for the line.

in cases where the actual direction matters though, you always want the components of your vector to be given by the components of the terminal point minus the components of the initial point

3. What if it doesnt state which one is the initial like this one

4. Originally Posted by usvn
What if it doesnt state which one is the initial like this one
Then it makes no difference which one you choose: Any direction vector will do. As Jhevon said, the order only matters in situations where the direction in which the line is traced out (i.e., its orientation) is important.