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HELP- Vectors Watch

1. Hello, my friend and I are completely stuck on part c of this vectors question.
"The straight line L1 and L2 have the vector equations r=(i+4j+2k)+t(8i+5j+k) and r= (I+4j+2k) +s(3i+j) respectively, and P is the point with the coordinates (1,4,2).
a) Show that the point Q lies on L1
b) Find the cosine of the acute angle between L1 and L1 [My friend and I both got 29/30 as the cosine of the acute angle]
c) Find the possible coordinates of the point R, such that R lies on L2 and PQ=PR"

We are very confused on this matter and can't find any questions/answers similar in order to try and work out how to solve this question. If anyone is able to help it would be very greatly appreciated.

Thank you very much.
2. What are the coordinates of Q?
3. (9,9,3)
5. For part c?
6. As B said, drawing a diagram does help with stuff like this, even if it looks a bit weird in 3D coordinates.

If you figure out the distance PQ = Q - P, then R - P should give you the same value.

The 2 things you will need here is the formula for the distance between 2 points and the general equation for a point on the line L2. You know R = [r1,r2,r3] = [1,4,2] + s[3,1,0] so you only really need to figure out what s could be to get the answers.
7. Okay, thank you, I have got the answers to be (10,7,2) and (-8,1,2).
8. No problem, I get the same

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Updated: February 20, 2016
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