Homework Help: Line Segment

1. Feb 23, 2009

cse63146

1. The problem statement, all variables and given/known data

Find the directed line segment joining (1,1,1) to (1,3,1)

2. Relevant equations

3. The attempt at a solution

(1,1,1) + (0,2,0)t is that correct?

2. Feb 23, 2009

Hurkyl

Staff Emeritus
Is it a directed line segment?
Does it start at (1,1,1)?
Does it end at (1,3,1)?

If so, then it's correct.

3. Feb 23, 2009

HallsofIvy

Notice the "start and stop". You will need conditions on t as well as, for the "directed" part, something like "as t goes from ___ to ___".

4. Feb 23, 2009

cse63146

you mean like this:

for all t $$\rightarrow \Re$$

or what im trying to say is that for all t that are real numbers (couldn't find the symbol for it; looks like a small 'e')

5. Feb 23, 2009

HallsofIvy

No, the whole point is that t cannot be "all real numbers". That could give the entire line, not the line segment. And you still haven't dealt with the "directed" part. Do you understand the difference between a line segment and a line? Do you understand what a directed line or directed line segment is?

Last edited by a moderator: Feb 24, 2009
6. Feb 23, 2009

cse63146

$$0 \leq t \leq 1$$

7. Feb 24, 2009

HallsofIvy

Okay, that gives the "segment". Now what about the "directed" part? Unfortunately, your original statement of the problem doesn't give a direction. You just said "the directed line segment joining (1,1,1) to (1,3,1)" which does not state a direction. Is the direction from (1, 1, 1) to (1, 2, 1) or from (1, 2, 1) to (1, 1, 1)?