B.O.B

I always come into class with a mind set that I know what I'm doing, but then when we start working on problems and you say to find the domain I totally forget everything I've learned about it. Its very confusing on how to write it down from wether I'm supposed to put a bracket or a the other one..? I just don't understand what to put down. I can easily solve an problem you give me it's just figuring out how to put down the domain and range.