JefferyL

a) We start by adding the first row of the grid. We set $S$ as $1+a+a^2+a^3...$ Then we set $a(S)$ as $a+a^2+a^3+a^4...$ because $a$ is the common ratio. From this, we can get $(a-1)S = -1$ which becomes $S = \frac{1}{1-a}.$ We observe that the second row...