# Direction of Electric Field lines

#### benmatt1999

Hello,
I understand how to get the magnitude for the electric field in this problem. My only issue is that I cannot figure out why the i coordinate is -sin while the j coordinate is -cos. I had the problem entirely right except I had cos in the i spot and sin in the j spot. I'm sure this is a very easy explanation, I just have been staring at it for a while and can't understand the logic behind it.

Thank you.

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#### topsquark

Forum Staff
Hello,
I understand how to get the magnitude for the electric field in this problem. My only issue is that I cannot figure out why the i coordinate is -sin while the j coordinate is -cos. I had the problem entirely right except I had cos in the i spot and sin in the j spot. I'm sure this is a very easy explanation, I just have been staring at it for a while and can't understand the logic behind it.

Thank you.
Two things.
1) The equation given for $$\displaystyle \vec{E}$$ (the first equation) shows a vector on one side and a scalar on the other. The idrection of $$\displaystyle \vec{E}$$ is radially outward from a positive point source. If you are dealing with a point source then you need to say that.

2) It is clear that you did not post the whole problem. Please do so, otherwise we can't help you with the question.

-Dan