Magnitude of electric field with square loop

[py208]

Homework Statement

The square loop shown below is made up of four identical wires of length scripted l = 18 cm each charged with a linear density λ = 18 nC/m.

Find the magnitude of the electric field at a distance z = scripted l/2 above the center of the loop.

Homework Equations

Start by first simplifying the result from problem 21-46,
E = (2kλ)(L/x)(4x2 + L^2)^-1/2
where x = (z^2 + (L/2)^2)^1/2. Then make use of the symmetry of the situation.

The Attempt at a Solution

I used this equation to solve and got 335.53967, But I don't know what to do after this, or if this number is even right. Help please!

 

[BvU]

Perhaps you want to show a bit more. Not numbers, but what variables stand for. I suppose (what else can I do) that 21-46 asks for the electric field on the Perpendicular Bisector of a charged rod ? this link, example 2.3 works that out very nicely.

Does that check with your 21-46 result ?
It looks to me as if your z is his (/her) y

I think I see a difference, so I might misinterpret the situatiuon.

Anyway, it simplifies a lot if z = L/2.

The next step is to add the four $\vec E$ with simple trigoniometry.