How to find magnitude/direction if no y-comp(Electric Field)?

anthony

New member
Is there another way to find direction? I'm doing a problem where there are 3 charges at each point of an equilateral triangle. I found the magnitude and direction for the top point. But for the bottom two, they have a y component of zero. How am I suppose to find the direction with tan^-1(y/x)?? Please help. Thanks.

http://session.masteringphysics.com/problemAsset/1083932/3/GIANCOLI.ch21.p13.jpg
 
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