Help Needed: Calculating Force Using Image Charges

[adamp121]

Hi,

I'm trying to use image charges to find the force that apply on the following particle (on the attachment) , but it seems that I do something wrong -
$F=2q^2/(2a^2)-2cos(60)q^2/a^2$
The gray section have 0 potential, so I've tried to put image charges like it is in the second attachment file.
Can someone help me?

Thanks,
Adam

 

[StarsRuler]

Graphics can help. But you must descript all the letters significance.¡¡¡ We are physics, not engineerings

 

[adamp121]

Sorry...
The upper and the lower charges are negative while the two middles are positive.