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Question 144 of 145

Q.Show that the lines rˉ=(i^+j^−k^)+λ(2i^−2j^+k^)\bar r=(\hat i+\hat j-\hat k)+\lambda(2\hat i-2\hat j+\hat k) and rˉ=(4i^−3j^+2k^)+μ(i^−2j^+2k^)\bar r=(4\hat i-3\hat j+2\hat k)+\mu(\hat i-2\hat j+2\hat k) intersect each other.

Maharashtra MsbshseMaharashtra HSC (MSBSHSE) Board 2026Subjective· 3mImportance★★★★★
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Equate the parametric coordinates of the two lines and solve for λ,μ\lambda,\mu; verify consistency in the third equation.

Line 1: rˉ=(1+2λ)i^+(1−2λ)j^+(−1+λ)k^\bar r=(1+2\lambda)\hat i+(1-2\lambda)\hat j+(-1+\lambda)\hat k

Line 2: rˉ=(4+μ)i^+(−3−2μ)j^+(2+2μ)k^\bar r=(4+\mu)\hat i+(-3-2\mu)\hat j+(2+2\mu)\hat k

For intersection, equate corresponding coordinates:

1+2λ=4+μ...(i)1+2\lambda=4+\mu \quad\text{...(i)}

1−2λ=−3−2μ...(ii)1-2\lambda=-3-2\mu \quad\text{...(ii)}

−1+λ=2+2μ...(iii)-1+\lambda=2+2\mu \quad\text{...(iii)}

From (i): μ=2λ−3\mu=2\lambda-3. Substituting into (ii):

1−2λ=−3−2(2λ−3)=−3−4λ+6=3−4λ1-2\lambda=-3-2(2\lambda-3)=-3-4\lambda+6=3-4\lambda

1−2λ=3−4λ  ⟹  2λ=2  ⟹  λ=11-2\lambda=3-4\lambda \implies 2\lambda=2 \implies \lambda=1

μ=2(1)−3=−1\mu=2(1)-3=-1

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