14. (a) According to the graph, when q3is very close to q1(at which point we can consider the force exerted by particle 1 on 3 to dominate) there is a (large) force in the positive xdirection. This is a repulsive force, then, so we conclude q1has the same sign as q3. Thus, q3is a positive-valued charge. (b) Since the graph crosses zero and particle 3 is betweenthe others, q1must have the
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