c
(c) \({F_2}\) \(=\) Force applied by \({q_2}\) on \( - {q_1}\)
\({F_3}\) \(=\) Force applied by \(( - {q_3})\) on \(-{q_1}\)
\(x-\)component of Net force on \( - {q_1}\) is
\(F_x = F_2 + F_3 sin\theta\) \( = k\frac{{{q_1}{q_2}}}{{{b^2}}} + k.\frac{{{q_1}{q_3}}}{{{a^2}}}\sin \theta \)
\(==>\) \({F_x} = k\,\left[ {\frac{{{q_1}{q_2}}}{{{b^2}}} + \frac{{{q_1}{q_3}}}{{{a^2}}}\sin \theta } \right]\)
\(==>\) \({F_x} = k \cdot {q_1}\,\left[ {\frac{{{q_2}}}{{{b^2}}} + \frac{{{q_3}}}{{{a^2}}}\sin \theta } \right]\) \(==>\) \({F_x} \propto \,\left( {\frac{{{q_2}}}{{{b^2}}} + \frac{{{q_3}}}{{{a^2}}}\sin \theta } \right)\)