@wonderer
Wonderer
commented
@binayaka-c Hi. In your answer you have:
#(-1)^(n-1)*5^(n-1)=15625#. Then it goes to:
#5^(n-1)=15625#
I am assuming then #(-1)^(n-1)=1#, but how can you be sure whether it is #-1# or #1# since you do not know the value of #n#. I just can't see how you can be sure of this. I know your answer is correct, but that part is puzzling me.
on
How do you find #S_n# for the geometric series #a_1=3#, #a_n=46,875#, r=-5?