1.

If the magnitude of sum of two vectors is equal to the magnitude of difference of the two vector, the angle between these Vector isA. `90^(@)`B. `45^(@)`C. `180^(@)`D. `0^(@)`

Answer» Correct Answer - A
(a) suppose two vector sr eP and Q . It is given that
`|P+Q|=|P-Q|`
Let angle between PandQ is `phi`
`therefore P^(2)+Q^(2) +2PQ cosphi=P^(2)+Q^(2)-2PQcosphi`
`implies4PQcosphi=0`
`implies cosphi=0 [thereforeP,Qne0]`
`=.phi=(pi)/(2) =90^(@)`


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