Hello ann2077210!

I assume that you'd like to begin the Calculus I course, and would like to know which concept in Calculus I students often struggle with. If that is so, students often struggle with the concept of variables .i.e x or h placement or that of a function as a result of the complex equations. 

However, if a student studying Calculus I daily after lessons, and having a solid knowledge of Math with determination and true optimism with confidence would find the Calculus I course less challenging, and can ace it. 

-Hope you understand,

~Galaxy