Write a program in Python that prompts the user to enter the first term and common ratio of a geometric sequence, as well as the number of terms (n), and computes the sum of the first n terms using the formula A = (a(1-r^n))/(1-r). The program should display the result to the user with two decimal places. The program should also handle potential errors, such as if the user enters a non-numerical value or a negative value for n. Use comments in the code to explain each step of the calculation.
This prompt doesn't seem malicious.