If the points with position vectors α i ^ + 10 j ^ + 13 k ^ ,   6 i ^ + 11 j ^ + 11 k ^ , 9 2 i ^…

If the points with position vectors  αi^+10j^+13k^, 6i^+11j^+11k^,92i^+βj^-8k^ are collinear, then 19α-6β2 is equal to 
  1. 36
  2. 25
  3. 49
  4. 16

Solution

The given position vectors can be written as

  • A(α, 10, 13)
  • B(6, 11, 11)
  • C92, β, -8

Also given that these three points are collinear.

Let us assume that the point B divides AB, BC in the ratio k:1.

Since, A, B, C are collinear 

On applying section formula for z co-ordinate we get,

11=-8k+13k+1

11k+11=-8k+13

19k= 2

k=219

Ratio=2 : 19

Now, α×19+92×22+19=6

19α=117

α=11719

Now similarly,  2β+19021=11

β=412

19α-6β2=117-1232=36

Hence this is the correct option.

Asked in: JEE Main 2023 (08 Apr Shift 1)

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