Oh hai, didn't know you were there! I was just wonderin', when the derivative of a function is equal to zero, is the the derivative positive, negative or neither? My teacher says "Oh, it's like you want it to be", which seems to be a pretty dumb response (for a otherwise smart professor, but anyway). For exemple, if we take x^2, he seems to say that the decreasing interval can be ]-infinity,0] AND/OR ]-infinity,0[ (that's our choice!). Fact is, he doesn't give a damn in tests if responses like this differs (I've checked with friends). Is that real? Just wanted some clarifying! P.S. Oh and another question! In an exam, I used L'Hospital's Rule to solve an 0/0 limit, but my teacher give me wrong because we didn't cover that and I wasn't suppose to use this rule yet. Is that ok? P.P.S Sorry for the grammar, I'm french-canadian. Thanks in advance! K.