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    				| 1. | The sides of a parallelogram are `2 hati + 4 hatj -5 hatk and hati + 2 hatj + 3 hatk `, then the unit vector parallel to one of the diagonals isA. `(1)/(7) (3 hati + 6 hatj - 2 hatk ) `B. `(1)/(7) (3 hati - 6 hatK - 2 hatk ) `C. `(1)/(7) (-3 hati + 6 hatj - 2 hatk ) `D. `(1)/(7) (3 hati + 6 hatj + 2 hatk ) ` | 
| Answer» Correct Answer - A Let ` vec a = 2 hati + 4 hatj - 5 hat k , vec b = hati - 2 hatj + 3 hat k .` The diagonals of the parallelogram are `vec p = vec a + vec b , vec q = vec b -vec a ` `rArr vecp =3 hati + 6 hatj - 2 hat k , vecq= - hati - 2 hatj + 8 hatk ` So, unit vectors along the diagonals are `(1)/(7) (3 hati + 6 hat j - 2 hatk ) and (1)/ (sqrt(69)) (-hati - 2 hatj + 8 hatk ) ` Hence, option (a) is correct. | |