completely lost here, any help appreciated.Quote:

Relative to a fixed origin, the points A, B and C have position vectors (2i − j + 6k),

(5i − 4j) and (7i − 6j − 4k) respectively.

(a) Show that A, B and C all lie on a single straight line.

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- May 7th 2010, 02:11 PMTweetyvector help, straight linesQuote:

Relative to a fixed origin, the points A, B and C have position vectors (2i − j + 6k),

(5i − 4j) and (7i − 6j − 4k) respectively.

(a) Show that A, B and C all lie on a single straight line.

- May 7th 2010, 05:02 PMSoroban
Hello, Tweety!

There are several ways to do this . . .

Quote:

Relative to a fixed origin, the points have position vectors:

. . (2i − j + 6k), (5i − 4j), (7i − 6j − 4k) respectively.

(a) Show that all lie on a single straight line.

We have: .

Then: .

The vectors are parallel and contain point

Therefore, the points are collinear.

Since , points are collinear.

We have: .

We have: .

Since , then: .

Therefore, points are collinear.