However, you must take notes, do exercises and listen to lectures. Otherwise it's you, no doubt.
Compared with science and engineering, it is generally more difficult for students majoring in economics and management to seek the limit (especially proving that the limit part may not be well understood) than for those majoring in liberal arts who think with sensibility.
Integral, however, is mainly a single integral. Remember the formula clearly, and you must be familiar with method of substitution and implicit function method, so that you can basically cope with the exam.
There seems to be no double integral, let alone triple integral.
I don't remember whether there are infinite series ... even if there are, the proportion should not be large.