Why is it saying that there is a syntax error for the if/else statement I wrote?

Question

I\'m trying to write a program that calculates the sum of a geometric series on a TI-84.

Prompt A

Prompt R

Prompt N

If N=100 and abs(R)<1

Disp (A/1-R)

El         


        

Answer 1

Else can only be paired with an If .. Then construct, not a plain If. So:

Prompt A,R,N
If N=100 and abs(R)<1
Then
Disp A/(1-R
Else
Disp (A(1-R^N))/(1-R

In general the If.. Then .. Else .. End construct should be closed by End but in this case the program exits anyway so it makes no difference. There is some documentation of this in the official TI-BASIC manual and you can check out a more detailed version here.