# MITx 6.002x week 9 – the school of hard sums

This week’s theme on 6.002x was hard sums. Second order differential equations to be precise. However, for anyone still struggling to get through the lectures, don’t give up! It turns out that most of what we’re expected to do is find the characteristic equations of second order circuits – and that’s all. Certainly none of the lab work or homework required any difficult calculus.

Being exposed to all the maths was simply meant to be good for the soul apparently. I suppose that it does make sense to have at least a vague understanding of why circuit problems involving resistors, inductors and capacitors can be solved using just the characteristic equation of second order differentials, even if all the maths made the lecture sequences for week 9 pretty daunting at first.

Something else I learned this week was that unlike the rest of the world, electrical engineers write the square root of -1 as j, rather than i. Seeing j used in this way had me reaching for my favourite Internet search engine to make absolutely sure that I hadn’t missed something important since I took maths A level! I guess that it makes sense to do this so that it doesn’t get confused with the symbol for current. On that basis, it makes it even more of a shame that the subtle but important differences between VI, vI, vi and Vi when scrawled in the hand of Professor Agarwal are often lost. One conclusion that I’ve already drawn from this course is that it’s amazing that any electronic circuits ever get built correctly, given the huge potential there is for errors in notation.

Anyway, I’m hopeful that there will be no more hard sums on this course. On second thoughts, that may be somewhat of a vain hope …