i apologise if this is the incorrect forum, i assume it would go under here or perhaps calculus forum - vector help!

http://upload.wikimedia.org/wikivers...ectorCross.png

find the formula for in terms of , and

thankyou so much in advance!

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- Jan 15th 2010, 10:32 PMiExcavatevector problem!
i apologise if this is the incorrect forum, i assume it would go under here or perhaps calculus forum - vector help!

http://upload.wikimedia.org/wikivers...ectorCross.png

find the formula for in terms of , and

thankyou so much in advance! - Jan 16th 2010, 12:13 AMtonio

This question belongs, me believes ,in trigonometry-analytic geometry. Anyway:

is an arrow beginning at and ending at and is its length, so using the cosines law (theorem) on the resulting triangle we get:

I'm not sure what is , but if you meant the dot product of these two vectors then just remember that , so you can substitute above.

Tonio - Jan 16th 2010, 12:42 AMiExcavate
how do i deduce

to prove:

- Jan 16th 2010, 01:49 AMHallsofIvy
tonio

**told**you: apply the cosine law to the triangle with sides a, b, and a- b.