The given G.P. is \[1,\text{ }-\text{ }a,\text{ }a2,\text{ }-\text{ }a3\text{ }\ldots \text{ }.\]
Here, the initial term \[=\text{ }a1\text{ }=\text{ }1\]
Furthermore, the normal proportion \[=\text{ }r\text{ }=\text{ }\text{ }a\]
We realize that,