The given G.P. is
![\[1,\text{ }-\text{ }a,\text{ }a2,\text{ }-\text{ }a3\text{ }\ldots \text{ }.\]](https://www.learnatnoon.com/s/wp-content/ql-cache/quicklatex.com-87406ed0985be5aff77906caafa7196d_l3.png "Rendered by QuickLaTeX.com")
Here, the initial term
![\[=\text{ }a1\text{ }=\text{ }1\]](https://www.learnatnoon.com/s/wp-content/ql-cache/quicklatex.com-db7933da9b791ac4c4d0e1842a8e0748_l3.png "Rendered by QuickLaTeX.com")
Furthermore, the normal proportion
![\[=\text{ }r\text{ }=\text{ }\text{ }a\]](https://www.learnatnoon.com/s/wp-content/ql-cache/quicklatex.com-05659caf02d0b7c6d9785bfdbec9a300_l3.png "Rendered by QuickLaTeX.com")
We realize that,
Find the sum to n terms in the geometric progression 1, -a, a2, -a3 …. (if a ≠ -1)
Find the sum to n terms in the geometric progression 1, -a, a2, -a3 …. (if a ≠ -1)