Final answer:
If the net force on q1 is zero, q2 and q3 must have equal magnitudes, but opposite signs.
Step-by-step explanation:
In order for the net force on q1 to be zero, the forces acting on q1 must cancel out. This means that the magnitudes of the forces exerted by charges q2 and q3 on q1 must be equal. Assuming the charges are point charges, the magnitude of the force between two charged particles can be calculated using Coulomb's law, which states that the force is proportional to the product of the charges and inversely proportional to the square of the distance between them. Therefore, if the net force on q1 is zero, q2 and q3 must have equal magnitudes, but opposite signs.