Question

Pls explain this example 7 solution i understood that chargers at all corners will be cancelled out except +7q and -7q that also i got
But when they calculated force there the charge is 7q both are taken as positive but there is one neagtive -7q can u explain me plssssss

Answer 1

While calculating force using Coulomb's law, only magnitude of the charge must be taken into consideration.

In this case +7q repels +q and -7q attracts +q, so the net direction of force is along -7q.