I'm taking an elementary differential equations class and we got our first exam back and...
I'm taking an elementary differential equations class and we got our first exam back and I don't understand why I was wrong on one of the questions. I got a 96, and the professor said there were quite a few d's and f's, so I didn't want to quibble about this.
Anyway, the problem was and I chose the sub , with and then plugged in the expression for , separated the equation and solved for y in terms of u and then substituted back to get The professor took issue with my expression for , saying that I couldn't differentiate y w.r.t. u if y is part of u. Is this correct?