Using Coulomb's Law
Problem: Find the force on the
charge at the origin.
Comment: See the diagram above.
The relative lengths of the forces drawn there are not intended to be to
scale. The subscripts on each indicate the charges that participate in
causing each force.
Solution: We use Coulomb's Law
twice to find each force...
The vector notation is essential
here - "find the force" means to include the direction, not just the magnitude
of the force.