3. How many terms of the series 17, 15, 13,.... amount to 72 ?
4. What is the number of terms in the series 5, 7, 9,.... if its su
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1
Answer:
5 is the answer may be helpful for you
Answered by
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Answer:
3) S=n/2[2a+(n-1)d]
72=n/2[2×17+(n-1)-2]
144=n[34-2n+2]
144=n(36-2n)
144=36n-2n^2
2n^2-36n+144=0
n^2-18n+72=0
n^2-6n-12n+72=0
n(n-6)-12(n-6)=0
(n-6)(n-12)=0
n=6 or 12
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