[" (15) Two charges "-q" and "+q" are located at points "(0,0,-a)" and "(0,0,a)" respectively."],[[" (a) What is the electrostatic potential at the points "(0,0,z)" and "(x,y,0)?,(r)/(a)>>1.],[" (b) Obtain the dependence of potential on the distance "r" of a point from the orgin the orgin,when "(r)/(a)>1.],[" (c) How much work is done in moving a small test charge,from the point "(5,0,0)" to "(-7,0,0)" along "X" -axis "2" Does "],[" the answer change if the test charge between the same two points is not along the X-axis? "]]