Misc 9 - Chapter 9 Class 11 Sequences and Series
Last updated at May 29, 2018 by Teachoo
Transcript
Misc 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 of G.P. It is given that Sum of third term & fifth term is 90 i.e. a3 + a5 = 90 We know that nth term of GP = arn – 1 i.e. an = arn – 1 Putting n = 3 & a = 1 a3 = 1 r3 – 1 = r2 Putting n = 5 & a = 1 a5 = 1.r5 – 1 a5 = r4 Putting a3 & a5 in (1) a3 + a5 = 90 r2 + r4 = 90 r4 + r2 – 90 = 0 Let r2 = x So, our equation becomes x2 + x – 90 = 0 x2 + 10x – 9x – 90 = 0 x(x + 10) – 9(x + 10) = 0 (x – 9)(x + 10) = 0 (x – 9)(x + 10) = 0 Hence the common ratio is -3 and 3
Miscellaneous
Misc 1
Misc 2
Misc 3 Important
Misc 4
Misc 5
Misc 6
Misc 7 Important
Misc 8
Misc 9 You are here
Misc 10
Misc 11
Misc 12
Misc 13
Misc 14
Misc 15
Misc 16 Important
Misc 17
Misc 18
Misc 19 Important
Misc 20
Misc 21
Misc 22
Misc 23
Misc 24
Misc 25 Important
Misc 26
Misc 27
Misc 28 Important
Misc 29
Misc 30
Misc 31
Misc 32 Important
Chapter 9 Class 11 Sequences and Series
Serial order wise
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