Aplastic rod 1.7 m long is rubbed all over with wool, and acquires a charge of -8e-08 coulombs. we choose the center of the rod to be the origin of our coordinate system, with the x-axis extending to the right, the y-axis extending up, and the z-axis out of the page. in order to calculate the electric field at location a = < 0.7, 0, 0 > m, we divide the rod into 8 pieces, and approximate each piece as a point charge located at the center of the piece.