1. The problem statement, all variables and given/known data Expand V(z + dz, t). I have seen problems like this in both my EnM and semiconductor courses but it's bothering me because I don't understand how the Taylor series is being used in this case... 2. Relevant equations 3. The attempt at a solution Taylor series: f(a) + f'(x-a) + .... let f = V(z+dz, t) Here is where I get stuck... I don't really know what to do I guess the first term: V(z,t) makes sense but the second term: dV(z,t)/dz delta(z) doesn't make any sense to me at all... What the heck happens in the second term?