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**1. Homework Statement**

The magnitude of each of the charges in the figure is 9.00x10^-12 C. The lengths of the sides of the rectangle are 3.00 cm and 6.00 cm. Find the magnitude of the electric field at the center of the rectangle in figures a and b.

http://www.webassign.net/CJ/18-21fig.gif

**2. Homework Equations**

E=kq/r^2

**3. The Attempt at a Solution**

For part A, I attempted to use the equation E=kq/r^2 to find the magnitude of E24 since that is all that is contributing to the electric field because of the fact that the charges at corner 1 and corner 3 are both positive and will cancel each other out. I used the pythagorean theorum to find the length of the hypotenuse (which I used as the r in the equation) of the right triangle that is created with the line between E24 and the sides of 3 cm and 6 cm to come up with a value of 6.708 which converts to .06708 meters.

E=[(8.99x10^9)(9.00x10-12)]/(.06708)^2 = 17.98 N/C I don't believe this answer is correct and this is where I have been stuck for the last few hours trying to figure out what I've done wrong.

For part B, I have no idea how to proceed because I will need the work from part A to go any further. Any guidance would be greatly appreciated!