1.

If the vector `-hati +hatj-hatk` bisects the angle between the vector `vecc` and the vector `3hati +4hatj,` then the vector along `vecc` isA. `(1)/(15)(11 hati + 10hatj + 2 hatk)`B. `-(1)/(15)(11 hati - 10hatj + 2 hatk)`C. `-(1)/(15)(11 hati + 10hatj - 2 hatk)`D. `-(1)/(15)(11 hati + 10hatj + 2 hatk)`

Answer» Correct Answer - D
Let `x hati + yhatj + z hatk` be the unit vector along `vec c`.
Since `-hati + hatj - hatk` bisects the angle between `vec c and 3 hati + hatj.`
`therefore lambda (-hati +hatj - hatk) = (xhati +yhatj + z hatk ) + (3hati +4hatj)/(5)`
`rArr x +(3)/(5) = - lambda , y+(4)/(5)=lambda and z= -lambda `
Now, ` x^(2) +y^(2) +z^(2) =1 " " [ because x hati + y hatj + z hatk " is a unit vector" ]`
` rArr (-lambda - (3)/(5))^(2) + (lambda-(4)/(5))^(2) + lambda^(2) =1 rArr lambda =0 or, lambda = (2)/(15)`
But, `lambda ne 0. " Because " lambda = 0` implies that the given vectors are parallel.
` therefore lambda=(2)/(15) rArr x = -(11)/(15) , y= - (10)/(15) and z = -(2)/(15)`
Hence, `xhati +yhatj + z hatk =-(1)/(15) (11 hati + 10hatj + 2hatk)` .


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