I recieved this question and don't really know where to start with it, any help would be much appreciated.. "The formula 1 + r + r^2 +..r(n-1) = 1-n/1-r is true for what values of r?"
"The formula 1 + r + r^2 +..r(n-1) = 1-n/1-r is true for what values of r?"
If I understand your meaning correctly, then look up the rules they gave you for the sums of infinite geometric progressions (series). For what values of "r" is this sum "defined"?