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A2 OCR C4 JUNE 2005 Vector Question help?

Basically, ABCD is a parallegram and you know what A,B and C are, and have to work out D.

A: 2i, j, 3k
B: 3i-2j
C: i-j-2k

I know that AB is parallel to CD, but still can't seem to work it out (too many unknowns)?

Edit:

I have x-1= k
y+1= -3k
z+2= -3k
(edited 8 years ago)
Reply 1
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Spriggs3
D: 0i, 2j, 1k
Reply 2
Avatar for popo111
popo111
OP
10
Original post by Spriggs3
D: 0i, 2j, 1k


How did you get to that?
Reply 3
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Spriggs3
WEll you know that AB and DC are parallel, so the difference in all coordinates between B and A will be the same as the difference in co-ordinates between C and D. So find the difference in coordinates (2i-3i=-i, j--2j=3j, 3k-0=3k), then add this to C (i-i=0i, -j+3j=2j, -2k+3k=k) to get D

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