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Question

Let r=a+λl and r=b=μm be two lines in space where a=5^i+^j+2^k,b=^i+7^j+8^k,l=4^i+^j^kandm=2^i5^j7^k then the p.v. of a point which lies on both of these lines, is

A
^i+2^j+^k
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B
2^i+^j+^k
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C
^i+^j+2^k
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D
non existent as the lines are skew
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Solution

The correct option is A ^i+2^j+^k
r1=a+λ^i
r1=(5^i+^j+2^k)+λ(4^i+^j^k)
r1=(54λ)^i+(1+λ)^j+(2λ)^k
r2=b+μm=(^i+7^j+8^k)+μ(2^i5^j7^k)
r2=(1+2μ)^i+(75μ)^j+(87μ)^k
Given r1 and r2 intersect at a part
(54λ)=(1+2μ)...(1) and (1+λ)=(75μ)...(2) and (2λ)=(87μ)...(3)
944λ=1+2μ
94(1+λ)=1+2μ
94(75μ)=1+2μ (from 2)
928+20μ=1+2μ
18μ=20μ=10/9
(1+λ)=75(109)
(1+λ)=139λ=1391
(λ=4/9)
(λ,μ)=(4/9,10/9)
Put (λ,μ) in (3)
LHS (24/9)=149
RHS 87(109)7270929
LHSRHS
There is no point that lies on both r1 and r2

1084143_1115600_ans_b89d55cf176e4164949a1d1901e42ecf.png

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