Consider three charges  $q_1, q_2$ and  $q_3$ each equal to q at the vertices of an equilateral triangle of side  $\text{'}l\text{'}$ what is the force on any charge due to remaining charges.

The forces acting on the charge ‘q’ are 

$$\begin{gathered} \overrightarrow{F_1}=\frac{1}{4\pi {\in }_0}\frac{q^2}{l^2} \\ \overrightarrow{F_2}=\frac{1}{4\pi {\in }_0}\frac{q^2}{l^2} \end{gathered}$$

Clearly $\left|\overrightarrow{F_1}\right|=\left|\overrightarrow{F_2}\right|=\left|F\right|$
The resultant force is  $F^1=\sqrt{F^2+F^2+2FF\cos {60}^0} =\sqrt{3}F=\sqrt{3}\frac{1}{4\pi {\in }_0}\frac{q^2}{l^2}$