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A positive charge (red) is shown along with a region blocked by a gray curtain (position is given in meters). The electric force on the positive charge is represented with a force vector. The region behind the gray curtain contains two charges of equal magnitude but unknown polarity (unknown sign). You can drag the red charge along the black circle. Restart.

Draw a picture showing the sign and location of each charge within the covered area.

Problem authored by Melissa Dancy.