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Vectors

Cool goIITian

Joined:	30 Jan 2008
Post:	92

25 Mar 2008 10:37:10 IST

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434

a quick one

None

whta is the projection of vector 4i-3j+k on the line joining point (2,3,-1) and (-2,-4,3)

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varsha valli g.

Blazing goIITian

Joined: 31 Jan 2007

Posts: 515

25 Mar 2008 11:50:49 IST

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let a'=4i-3j+k

b'=(2+2)i+(3+4)j+(-1-3)k
=4i+7j-4k
mod b'=9
b"means unit vector of b'

projection=d=a'.b"
=a'.b'/mod b'
=(16-21-4)/9
=-1

hope this helps
!!!!!!!!!!!!!!!

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Scorching goIITian

Joined: 11 Mar 2007

Posts: 268

25 Mar 2008 11:51:50 IST

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(2,3,-1) and (-2,-4,3)-DIS IS POSITION VECTOR.
FIND LINE PASSING THRU DIS.
IT IS -4i +-7j+4k
NW PROJECTION WILL BE
{(4i-3j+k).(-4i -7j+4k)}/

81=
=(-16+21+4)/9
=1

BILLA

Blazing goIITian

Joined: 14 Mar 2008

Posts: 447

25 Mar 2008 12:06:54 IST

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i too think the answer is one coz see you know the drs of the line joining the two pints and the now do the dot product of the two vectors effectively the corresponding drs product and then divide by root 81 to get the answer

the answer comes to be 1

@ varsha villag: your approach is rite but use modulus as projection is always positive!!!!

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