I am not doing well in Engineering and I don't know why. Advice please?

[bodangles]

Go through the derivations for each formula. Draw trapezoids under your function and use that to derive the integral formulas so that you understand them. Then you will be in a better position to handle more complicated problems.

The problem with college classes is that they often move too fast to make this a feasible solution. On a test you just need to know the rule, not spend time deriving it.