Stuck on this one electric field problem

[vitaebellaa]

Homework Statement

Homework Equations

E=k*Q/r^2

The Attempt at a Solution

Ey=E1sin30 + E2sin30 + E3; where E1=E2 (I'm denoting the 2 bottom charges as E1,E2, the negative as E3)
Ex=E1cos30 - E2cos30, this cancels.
from E=k*Q/r^2
I calculated r^2 to be L^4/4 (don't know if this is right... trig. and I haven't really been on speaking terms since high school)
since sin30=1/2... E1(1/2) + E2(1/2) just equal (1)E1; E1=k*Q/(L^4/4)
I guess from there I would have to add the y component of E3, which would be k*Q/(L^2/4)
Is my math/'plan of attack' okay so far? Is the next step simply adding E1 + E3 and simplifying?

THANK YOU!

 

[tiny-tim]

hi vitaebellaa!

yes that's the correct method (obviously, you meant L² not L⁴) …

for r, draw a right-angled triangle with length L/2