The first term of a G.P. is 1. The sum o | Class 11 Mathematics Chapter Sequence and Series, Sequence and Series NCERT Solutions

Question:

The first term of a G.P. is 1. The sum of the third term and fifth term is 90. Find the common ratio of G.P.

Answer:

Let a and r be the first term and the common ratio of the G.P. respectively.

∴ a = 1

a₃ = ar² = r2

a₅ = ar⁴ = r4

∴ r² + r⁴ = 90

⇒ r⁴ + r² – 90 = 0

$rightwards double arrow r squared space equals space fraction numerator minus 1 space plus space square root of 1 plus space 360 end root over denominator 2 end fraction equals fraction numerator minus 1 space plus-or-minus square root of 361 over denominator 2 end fraction equals fraction numerator minus 1 plus-or-minus 19 over denominator 2 end fraction equals minus 10 space o r space 9$

∴ r = ± 3 ( Taking real roots)

Thus, the common ratio of the G.P. is ±3.

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Comments

Subhangi Manisha Mohanty
2019-04-18 07:51:07

Thanks for your answer.i love it thanks once again ððððððð

Samyuktha
2018-12-11 19:21:24

Can u write in equation form

sree
2018-08-30 22:06:52

Tqððð

Mokshagna
2018-05-20 10:05:18

Can you plese detail answer

Mokshagna
2018-05-20 10:03:32

How it will come

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Welcome to the NCERT Solutions for Class 11 Mathematics - Chapter . This page offers a step-by-step solution to the specific question from Excercise 5 , Question 9: The first term of a G.P. is 1. The sum of the third term and fifth term is 90. Find the common ratio....

The first term of a G.P. is 1. The sum o | Class 11 Mathematics Chapter Sequence and Series, Sequence and Series NCERT Solutions

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