The given points are P(1,2,3) and Q(4,5,6)​∴PQ​=(4−1)i^+(5−2)j^​+(6−3)k^=3i^+3j^​+3k^∣PQ​∣=32+32+32​=9+9+9​=27​=33​​ Hence, the unit vector in the direction of PQ​is ​ ∣PQ​∣PQ​​=33​3i^+3j^​+3k^​=3​1​i^+3​1​j^​+3​1​k^