1.

Show that the lines `(x-1)/(3)=(y+1)/(2) =(z-1)/(5) " and " (x+2)/(4)=(y-1)/(3)=(z+1)/(-2)` do not intersect .

Answer» The given lines are
`(x-1)/(3)=(y+1)/(2)=(z-1)/(5)= ` (say)
`(x+2)/(4) =(y-1)/(3)=(z+1)/(-2) = mu` (say)
The general point on (1) is `P(3lambda+ +1,2lambda-1,5lambda+1)`
The general point on (2) is Q `(4mu -2, 3mu +1, -2mu -1)`
If possible let the given lines intersect .
Then P and Q coincide for some particular values of `lambda` and `mu`
In that case we have
`3lambda +1 =4mu -2, 2lambda -1 , =3mu +1 " and " 5lambda +1 =-2mu -1`
`hArr 3lambda -4mu =-3 ...(i) ,2lambda -3mu =2 ....(ii) ,5lambda +2mu =-2 .....(iii)`
solving (i) and (ii) we get `lambda =-17 " and " mu=-12`
However these values of `lambda " and " mu ` do not satisfy (iii)
Hence the given lines do not intersect .


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