1. The problem statement, all variables and given/known data Question: ____________________________________________________________________________________ And the answer in the solution manual: 2. Relevant equations Trig sub? [tex]a^2/x^2 = tan(θ) [/tex] I'm thinking x>>a would affect this majorly and I'm not seeing how. 3. The attempt at a solution I understand the concept behind this (I think), but part c is killing me right now. I have no idea how the inverse square root turns into the final equation. Maybe I should have posted this in Calculus, but I have no recollection of learning this in calc I/II, nor physics I/II so I didn't know where to post. The [tex]a^2/x^2[/tex] looks eerily similar to a trig sub problem, but I don't see how that would work because there's no integral. For [tex]E_x,[/tex] I was able to set the limit of a to 0 to get the point charge equation. The solution manual didn't do it this way but it worked for me to get the point charge equation. BTW I already have a) and b), which were pretty straightforward. Could someone point me in the right direction please? Thank you!