For each of the following arrangements of two point charges, find all the points along the line passing through both charges for which the electric potential V is zero (take V = 0 infinitely far from the charges) and for which the electric field E is zero:
(a) Charges +Q and +2Q separated by a distance d, and
(b) Charges -Q and + 2Q separated by a distance d.
(c) Are both V and E zero at the same places? Explain.