The sum of infinite number of terms of a GP is 4, and the sum of their cubes is 192. Find the series.
The following image is solution from my book.
My doubt is why is $r=-2$ rejected? Is there any reason. If so please tell me.
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Given GP, is infinite and the sum is finite in two given conditions. So for the finite sum to exist for an infinite GP the magnitude of the common ratio must be less than one. If you have further doubt please ask in the comments below.
Vishnu
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