Question

If mi+2mj is a unit vector, then the value of ‘m’ is A. 1/√3 B.1/√2 C.1/√ 5 D.1/2

Answer 1

|m i + 2m j| = sqrt(m^2 + (2m)^2) = sqrt(5m^2) = sqrt5 |m| = 1, so |m| = 1/√5.
Hence m = ±1/√5; from the choices the positive value is 1/√5 (C).