અલગ અલગ સમતલના કેટલા સદિશોનો સરવાળો કરતાં

 The required number of vectors is $4.$ suppose $A, B, C, D$ are four vectors and no three of them are coplaner. if the resultant of $\mathrm{A}$ and $\mathrm{B}$ be $\mathrm{X},$ and resultant of $\mathrm{C}$ and $\mathrm{D}$ be $\mathrm{Y}$. if $\mathrm{X},$ and $\mathrm{Y}$ be equal in magnitude but in opposing directions, that's the only way the resultant of $A, B, C, D$ be zero, without any three of them being in the same plane.