NCERT Class 11 Mathematics Solutions: Chapter 9 – Sequences and Series Miscellaneous Exercise 9 Part 6 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Sum of a Geometric Series

1. A G. P. consists of an even number of terms. If the sum of all the terms is times the sum of terms occupying odd places, then find its common ratio.


Consider the G. P. be .

Number of terms

According to the given condition,

Consider the G. P. be

So, the common ratio of the G. P. is .

2. The sum of the first four terms of an A. P. is . The sum of the last four terms is . If its first term is , then find the number of terms.


The A. P. be a, .

Sum of first four terms

Sum of last four terms

According to the given condition,

[Since (given) ]

So, the number of terms of the A. P. is