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To achieve equilibrium for the third charge q3 placed between two fixed point charges q1 and q2, we need to consider the forces acting on q3. The sign of q3 will indeed depend on the signs of q1 and q2.

1. If  q1and q2 have the same sign (both positive or both negative), q3 should have an opposite sign to either charge in order to experience attractive forces from both sides, balancing the net force to zero.

2. If q1 and q2 have opposite signs (one positive and one negative), q3 can have either sign, but for stability, placing q3 closer to the weaker charge (the one with the smaller magnitude) would generally help maintain equilibrium.

Therefore, the determination of the sign of q3 is crucial for achieving the desired equilibrium based on the configuration of the other charges. If you have any further questions or need assistance with related topics, feel free to ask!