Physics - Vectors Question with Solution | TestHub

This is an important result to remember. Two vectors at 120 degree produce a vector equal to their magnitude. Let their magnitude be a, $$\begin{array}{l}\text{ Resultant }=a=\sqrt{\left(a^2+a^2+2\times a\times a\times \cos \theta \right)}=a\sqrt{(2+2\cos \theta )}\Rightarrow \cos \theta =-\frac{1}{2}\\ \Rightarrow \theta =120^0\end{array}$$