\(\because \quad \vec{F}_{A B}=0\)
The net magnetic force on a current carrying closed loop in a uniform magnetic field is zero.
\(\therefore \vec{F}_{A B}+\vec{F}_{B C}+\vec{F}_{A C}=0\)
\(\Rightarrow \vec{F}_{A C}=-\vec{F}_{B C}\) \(\left(\because \vec{F}_{A B}=0\right)\)