# Thread: Need help with some of the vector question, especially part c, and e-h

1. ## Need help with some of the vector question, especially part c, and e-h

Suppose a point A has co-ordinates (−1, 3, 5), a point B has co-ordinates
(0, −3, 2), and another point C has co-ordinates (−5, −5, −5).
(a) Find −→BA and −−→CB.
BA(1, 0, -7)
CB(5, 8, 3)
(b) Find −→BA − 3
−−→CB.
(16, 24, 16)
(c) Use the result of part (b) to write −→BA − 3
−−→CB as a multiple of the vector (8, 0, 9).??? DON'T GET THIS PART

(d) Express −−→CB in terms of the standard unit vectors i, j and k.
-5i-8j-3k
(e) Use the result of part (a) to ﬁnd −→AC.
(f) Verify the triangle inequality: ||−→AB +
−−→BC|| ≤ ||−→AB|| + ||−−→BC||.
(g) Find a unit vector pointing in the same direction as −→AB.
(h) How far is the point C from the origin?

2. ## Re: Need help with some of the vector question, especially part c, and e-h

If you could rewrite your questions using LaTeX, that would be great. For example, use
Code:
$\overrightarrow{BA}-3\overrightarrow{CB}$
for
$\overrightarrow{BA}-3\overrightarrow{CB}.$
I don't understand what dashes (sometimes one, sometimes two in a row) are supposed to mean. Also, it is recommended to ask at most two questions in a thread.

3. ## Re: Need help with some of the vector question, especially part c, and e-h

Originally Posted by Fearsword
Suppose a point A has co-ordinates (−1, 3, 5), a point B has co-ordinates
(0, −3, 2), and another point C has co-ordinates (−5, −5, −5).
(a) Find −→BA and −−→CB.
BA(1, 0, -7)
CB(5, 8, 3)
To begin with these are wrong. Pleas show each individual calculation.
Once you have those wrong, you can't hope to get the rest right.

B](b) Find −→BA − 3[/B]
−−→CB.
(16, 24, 16)
(c) Use the result of part (b) to write −→BA − 3
−−→CB as a multiple of the vector (8, 0, 9).??? DON'T GET THIS PART

(d) Express −−→CB in terms of the standard unit vectors i, j and k.
-5i-8j-3k
(e) Use the result of part (a) to ﬁnd −→AC.
(f) Verify the triangle inequality: ||−→AB +
−−→BC|| ≤ ||−→AB|| + ||−−→BC||.
(g) Find a unit vector pointing in the same direction as −→AB.
(h) How far is the point C from the origin?