Magnitude of net electric field

[mayo2kett]

Four point charges have the same magnitude of 2.2 10-12 C and are fixed to the corners of a square that is 3.0 cm on a side. Three of the charges are positive and one is negative. Determine the magnitude of the net electric field that exists at the center of the square.

i tried using E=(k|q|)/r^2 but it wasn't working and I'm not sure how to combine the electric fields for all of the outside charges...

-annie

 

[Jelfish]

Why doesn't that formula work?

 

[mayo2kett]

this is what i tried ((8.99e9)(2.2e-12))/((3.0e-2)^2) and i got 21.976... so now am i supposed to multiply by 4? cause that answer i got isn't right
-annie

 

[mayo2kett]

ahha i figured it out... :)