# Stuck on a vectors question! (C4)

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#1
okay so the question is:
'Find the cosine of the angle between the lines r=-i+2j+3k+s(4i+j-k)
and r=2i-3j+4k+t(-i+6j+2k)'
I'm not really sure where to start, do I find the point of intersection?
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#2
please? 0
5 years ago
#3
(Original post by phoebeg76)
okay so the question is:
'Find the cosine of the angle between the lines r=-i+2j+3k+s(4i+j-k)
and r=2i-3j+4k+t(-i+6j+2k)'
I'm not really sure where to start, do I find the point of intersection?
No need to find the point of intersection. You want to find the cosine of the angle between the directions of the line's, if that makes sense. So use the dot product to find the cosine of the angle between the lines, using the direction vectors.

It's well explained on this video if it still doesn't make sense: http://www.examsolutions.net/maths-r...tutorial-1.php 0
#4
(Original post by usycool1)
No need to find the point of intersection. You want to find the cosine of the angle between the directions of the line's, if that makes sense. So use the dot product to find the cosine of the angle between the lines, using the direction vectors.

It's well explained on this video if it still doesn't make sense: http://www.examsolutions.net/maths-r...tutorial-1.php Thank you so much! The video really helped, I realised I was using the position vectors instead of the direction vectors!
Thanks again 0
5 years ago
#5
...Reason why I'm not doing A2 Maths... 0
#6
(Original post by BCMFM16)
...Reason why I'm not doing A2 Maths... I'm only in year 12, taking further maths so we take AS and A2 maths in year 12, and AS and A2 further maths in year 13....
probably not my best decision to be honest haha
0
5 years ago
#7
(Original post by phoebeg76)
I'm only in year 12, taking further maths so we take AS and A2 maths in year 12, and AS and A2 further maths in year 13....
probably not my best decision to be honest haha
Oh ok lol Good luck anyway!!
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