Answer:

Step-by-step explanation:
The sum you are trying to understand is this.

Remember that in general when you have a geometric series
you have that
and that equality is true as long as
.
Therefore here we have
and 
Therefore we can use the formula and

First Column, -x and 5 third column, -x and 2
Y is 13 when you solve the problem
Answer:
i do not know sorry (^_^) :(