I'm currently learning integral calculus, in particularly, integral function with the lower bound been the variable and upper bound is the constant.
Below is a question and solution from khan academy
My question is,
can't we just work with the lower bound being the variable (i.e. upper bound is a constant and lower bound is a variable that changes) instead of switching the upper and lower bound (so that variable bound is the upper bound) and then add a negative sign?
It seem to me that enforcing the lower bound to be a constant and upper bound to be a variable that changes, is somewhat artificial (unless there is some fundamental difference between the two scenario that I haven't understood yet).