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### Question Asked by a Student from EXXAMM.com Team

** Q 2127078881. ** If `P, Q, R, S` are the points `(2, 3, -1), (3, 5,- 3)`,

`(1, 2, 3), (3, 5, 7)` respectively. Then the projection of `PQ`

on `RS` is ......... and hence `PQ` and `RS` are `........................ ..`