# Sum of points on the line

• May 15th 2010, 03:30 PM
joker40
Sum of points on the line
Hi,
I have lines such as that first line has 2 point (1,0,-1) and (4,1,-3) and when i check the sum which is (5,1,-4) it is not on the line.
Then I have line that has (2,-1,3) and (10,-5,15) and its sum is (12,-5,15) is on the line. I was wondering why the sum in some cases is on the line and in some it is not.
• May 15th 2010, 04:02 PM
skeeter
Quote:

Originally Posted by joker40
Hi,
I have lines such as that first line has 2 point (1,0,-1) and (4,1,-3) and when i check the sum which is (5,1,-4) it is not on the line.
Then I have line that has (2,-1,3) and (10,-5,15) and its sum is (12,-5,15) is on the line. I was wondering why the sum in some cases is on the line and in some it is not.

it works because one of the points is a scalar multiple of the other ...

5(2,-1,3) = (10,-5,15)
• May 15th 2010, 04:21 PM
joker40
yes but.....
Yes exactly. We are talking here about the point not vector scalars. those are just point not vectors. I didnt know we can take scalar of points....My assumption is that if we have vector for example (1,2,3) then any vector k(1,2,3) is on same line...
am i correct?
• May 15th 2010, 04:52 PM
skeeter
Quote:

Originally Posted by joker40
Yes exactly. We are talking here about the point not vector scalars. those are just point not vectors. I didnt know we can take scalar of points....My assumption is that if we have vector for example (1,2,3) then any vector k(1,2,3) is on same line...
am i correct?

yes
• May 15th 2010, 05:02 PM
joker40
but....?
but those values are point not vectors.
• May 15th 2010, 05:11 PM
skeeter
Quote:

Originally Posted by joker40
but those values are point not vectors.

but they behave the same way as vectors ... draw a line from the origin to the point.