First slide
Equation of line in Straight lines
Question

A line l passing through the origin is perpendicular to the lines l1:(3+t)i^+(1+2t)j^+(4+2t)k^, <t< l2:(3+2s)i^+(3+2s)j^+(2+s)k^, <s< Then, the coordinates (s) of the point (s) on l2 at a distance of 17 from the point of intersection of l and lt is (are)

Moderate
Solution

The given lines are l1:x31=y+12=z42=tl2:x32=y32=z21=s

Let direction ratios of l be a,b,c then as ll1 and l2

a+2b+2c=0

2a+2b+c=0

a2=b3=c2

l:x2=y3=z2=λ

Any point on l1 is (t+3,2t1,2t+4) and any point on l is (2λ,3λ,2λ)

 For Intersection point P of l and l1

t+3=2λ,2t1=3λ,2t+4=2λ

t=1,λ=1P(2,3,2)

Any point Q on l2 is (2s+3,2s+3,s+2)

As per question PQ=17

(2s+1)2+(2s+6)2+s2=17

9s2+28s+20=0s=2,109

Point Q can be (-1,-1,0) and 79,79,89

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