Non-parallel Plate Capacitor

1. The problem statement, all variables and given/known data
A capacitor has square plates, each of side a, making an angle theta with eachother. Shown that for small theta the capacitance is given by: C = [(epsilon)(a^2)/d][1-(a(theta)/2d].

2. Relevant equations
C = q/V
gauss' law

3. The attempt at a solution
I see how you can divide up the strip into N segments each with length a/N. But how do u get the capacitance for each strip to be C = (epsilon)a(deltax)/y ? I know how to do the rest and I know for sure that that's the right way to do it, but how do u get the capacitance for each strip?)
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 See that C = $$\epsilon$$*S/d, in your case for each strip S = a*dx and d = y.
 I'm also troubled with this question, I know it has been a long time, but maybe one of you can explain me the answer? Omer