Approximate Integration - further comments on the program

One of the other things to note about this program is that I have had to reuse several of the memory variables. The fx-50F comes with six memory variables (A, B, C, D, X and Y) and one independent memory (M) but this was not sufficient for the purposes of the program. For example, I calculate the value of the x-ordinate and store it in memory variable X, but then immediately calculate the y-ordinate, x², and store that in memory X too. This can be done because the x-ordinate is not needed after the y-ordinate has been calculated.