Electric charges of $1\; \mu C, \; 1 \; \mu C$ and $2 \mu C$ are placed in air at the corners of $A, B$ and $C$ respectively of an equilateral triangle $ABC$ having the length of the side $10\;cm$. The resultant forces at $C$ is : <br> $\begin{pmatrix} \frac{1}{4 \pi \varepsilon_0} = 9 \times 10^9 \frac{N m^{2}}{C^2} \end{pmatrix}$
