Q.

Let the point (1, α, β) lie on the line of the shortest distance between the lines x+23=y24=z52 and x+21=y+62=z10. Then (αβ)2 is equal to _________.          [2024]


Ans.

(25)

Let L1 : x+23=y24=z52 and L2 : x+21=y+62=z10

Let P(3λ2,4λ+2,2λ+5) be point on L1 and Q(μ2,2μ6,1) be point on L2.

Direction ratios of PQ(3λμ,2μ4λ8,2λ4)

Also, PQ=|i^j^k^342120|=4i^2j^2k^

i.e.2i^+j^+k^

 3λμ2=2μ4λ81=2λ41

 3λμ=4λ8 and 2μ4λ8=2λ4

 μ=7λ+8 and μ=λ+2

 λ=1 and μ=1

  Equation of PQ is, x+32=y+41=z11

Now, (1, α, β) lies on PQ

 1=α+4=β1

 α=3, β=2

  (αβ)2=25.