I was in my Grade $12$ Calculus class today and we were learning about how to find the area under a curve. It included a lot of the questions of the type, "Find the area of the curve $f(x)$ from $x = ...$ to $x = ...$, bounded by the $x$-axis" and "Evaluate the following definite integral using the Fundamental Theorem of Calculus".
My teacher then said, "For your homework questions, don't always assume that the curve meets the $x$-axis." What does he mean by this? I don't really understand.