Am I the only one saddened by the fact that this would have been a piece of cake back in high school/college, but can't remember how to do them (integrals) anymore? :(
>if you learned them once you can learn them again
I doubt this personally. I didn't have any problems with the partial differential I was set. I mean on a general level that something once learnt can be relearned.
You may not be as sharp at it as you were when you spent hours pounding it into your head on a frequent basis, but it's surely within a person's grasp. At least as far as math goes; something like language fluency may be another story.
I did a lot of maths in college before I moved onto programming and computer science, but I also found the problem hard. I think I could probably work it out from first principles eventually, but it's surprising how much calculus and trig comes down to memorising rules.