I remember having to learn that expression in Maths when I was about sixteen. It is actually
The first term is x^0/0! and the second term is x^1/1!
I have added code tags as Stephan suggested and you can see how much better it is to read.
You need to keep track of the division; eventually it will become vanishingly small, or you get ∞, in both of which cases you will have to stop your iteration
I think you are supposed to pass different values for n to the myexp() method, and the same value of x. The 'e'and 'f' parts are similar, but you pass different values of x.
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