posted by nikita .
three equal and similar charges each of 'q' units are placed at the corners of the square of side 'a' .find the electric field strength at the fourth corner?
E=kq/r^2 and in the direction of r.
Add these as vectors. If you are careful, you can use symmetry to simplify it.
Here is a similar question on the symmetry issue. http://www.jiskha.com/display.cgi?id=1270726327
Can you please Explain and Show the answer ?