Vectors

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|a|=2,a.b =1,angle between a and b = 60 . r is any vector satisfying:

r.a=2
r.b=8

(r+2a-10b).(a x b) = 4√3
(r+2a-10b) = Î»(a x b)

then Î» =

A)1/2
B)2
C)1/4
D)4

#Mathematics #Co-ordinate Geometry

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6 Answers

1

Vivek ·2009-02-24 07:04:35

anyone?

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33

Abhishek Priyam ·2009-02-24 07:43:37

|a||b|cos(60⁰)=1
|b|=1

Let r=la+mb+naxb

(la+mb+naxb).a=2
l|a|²+ma.b=2
4l+m=2

also r.b=8
(la+mb+naxb).b=8
la.b+m|b|²=8
l+m=8

solve for l and m
l=-2 m=10

also
(r+2a-10b).(a x b) = 4âˆš3
(-2a+10b+naxb+2a-10b).(axb) = 4√3 ..putting value of l and m

n|(axb)|²=4√3
n(√3)²=4√3
n=4√3/3

Î»=4√3/3

none matching... may be some calculation mistake

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33

Abhishek Priyam ·2009-02-24 07:46:49

but i can find no mistake in this.. may be options wrong... :O

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1

Vivek ·2009-02-24 08:38:12

i got the same answer you got,thats why i posted here

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33

Abhishek Priyam ·2009-02-24 09:17:47

options are wrong then.. :)

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1

Vivek ·2009-02-25 07:49:33

possible,very much possible coz the src is fiitjee

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