1.

If the position vectors of P and Q are `hati+2hatj-7hatk` and `5hati-3hatj+4hatk` respectively, the cosine of the angle between `vec(PQ)` and z-axis isA. `4/sqrt(162)`B. `11/sqrt(162)`C. `5/sqrt(162)`D. `-5/sqrt(162)`

Answer» Correct Answer - B
`vec(PQ)=vec(OQ) - vec(OP) = 4hati-5hatj+11hatk`
`therefore (vec(PQ))/(|vec(PQ)|)= 4/sqrt(162) hati - 5/sqrt(162)hatj + 11/sqrt(162)hatk`
`therefore coslambda=11/sqrt(162)`, where `lambda` is the angle of `vec(PQ)` with z-axis.


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