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Vectors

Scorching goIITian

Joined:	23 Oct 2007
Post:	234

19 Mar 2008 12:14:07 IST

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369

simple vector question

None

Find |a-b| if |a|=2 |b|=3 a.b=4

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Akhil

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Joined: 17 Jan 2008

Posts: 1451

19 Mar 2008 12:15:52 IST

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2x3xcosA=4
cosA=2/3

so we have
|a-b|=root(4+9-2*2*3*2/3)
=root(13-8)=root5

arpan1

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Joined: 15 Mar 2008

Posts: 684

19 Mar 2008 12:16:15 IST

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this is simple enough

cos ? = 2/3

then mod (a-b) = sqrt. (a²+b² -2ab cos ? )

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Halo

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Joined: 18 Apr 2007

Posts: 1537

19 Mar 2008 14:16:08 IST

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| a-b |² =(a-b).(a-b)
          =a.a-a.b-b.a+b.b
         =|a|² +|b|² -2a.b
         =4+9-8
         =5
|a-b|=

5

..............

Anand Krishnan

Hot goIITian

Joined: 5 Jul 2007

Posts: 104

19 Mar 2008 14:18:32 IST

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|a-b|=sqrt(|a|²+|b|²-2(a.b))
=sqrt(4+9-8)
=sqrt(5).

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