Calculus is hard, and the level of difficulty depends on the individual student. A student who is not well-versed in the prerequisites for calculus may find the subject more difficult than someone who has strong mathematical preparation.
Calculus covers topics like the slope of a function and the area under the graph of a function. Thus, students who have an excellent understanding of functions are less likely to have trouble learning calculus. Precalculus courses usually cover trigonometric functions, polynomial functions and the inverses of functions.
A function is a mathematical rule that accepts some value as an input and produces a corresponding value as its output. A student can display the outputs on a graph, and the outputs sometimes form a line or curve.