Point charge a is located at point a and point charge b is at point b. points a and b are separated by a distance r. to determine the electric potential at the mid-point along a line between points a and b, which of the following mathematical approaches is correct? a. the difference in the absolute value (the sign of the charges does not enter into the calculation) of the two electric potentials is determined at a distance r/2 from each of the charges. b. the algebraic sum of the two electric potentials is determined at a distance r/2 from each of the charges, making sure to include the signs of the charges. c. the electric potential due to each charge is determined at a distance r/2 from each of the charges and an average is taken of the two values. d. the vector sum of the two electric potentials determines the total electric potential at a distance r/2 from each of the charges