Advanced Flash Question: Dividing Strings

Hi,

Ok, I'm not sure if this can be done at all, but can i create a program that can understand and divide these strings:

2*x + 1
7cos(x)

and actually understand the x's and be able to enter values into it and get the corresponding y.

basically, i have to make a calculator for a school project. can the user input 2*x + 1 and the computer gives the answer for the equation at x = 200.

Can it be done? just give me a hint

Thanks in advance!