If you are wanting to prompt a imput then it would be:

?->A

? prompts the user to imput a value and that value will be stored into A for later calculations.

Example program

?->A

?->B

A+B

////

If that is not what you are wanting and are wanting to replace sin(2*pi*n) then I think you would want to do an if function:

If P=sin(2*pi*n)

Then 1->P

If P=cos(2*pi*n)

Then 0->P

Sorry again if thats not what you wanted, I don't think there is an exact function that will replace it but you can use the If statements.

thank u again

I found an ugly way to do that ))

for relapsing just cos(k.n.π)=1 jast for k=2 to 6 step 2

(2/T)×∫(f1[i,1]×cos(((2π×n)/T)×x),x,c,T)⇒an
for 2⇒i to 6 step 2
cos(i*n*π)⇒co
ExpToStr co,co
1⇒s1
while s1>0
ExpToStr an,s
strsrc s,co,s1
if s1=0 :then
goto a
ifend
strleft s,s1-1,left
strjoin left,"1",left
strlen s,len
strright s,len-(s1+9),right
strjoin left,right,s
strtoexp(s)⇒an
Lbl a
whileend
next

but its not a good cod :| I had to do this ring for sin() and I had to do it like 6 times in a program to get all I want!(for 3 variables like "an")

I hope someone has a better idea!