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(#M40037940) BOOK Category question series Keep an EYE

1+9+24+46+...

Asked In Book Prakash kumar (10 years ago)

Unsolved Read Solution (6)

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RAKESH  (10 years ago)

S = 1+9+24+46+...
S = 1+ 9+24+46+...
--------------------------------------------------
S – S = 1 + 8 + 15 + 22 + ... n terms - Tn
=> Tn = n/2[2 + (n-1)7] = (7n^2 – 5n)/2
=> S = ∑Tn = [7*∑n^2 - 5*∑n]/2
= 7n(n+1)(2n+1)/12 – 5n(n+1)/4
= n(n+1)/4 *(14n + 7 – 15)/3
=> S = n(n+1)(7n-4)/6

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paramvir  (10 years ago)

9-1=8
24-9=15 //8+7=15
46-24=22 //15+7=22
NEXT NO.=22+7+46=75

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Pragya Ranka  (10 years ago)

75...
because
9-1=8
24-9=15
46-24=22
so now,
8-15=7
15-22=7
there is common difference that is 7
22+7=29
after that add this 29 with 46
29+46=75

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umabhargavi  (10 years ago)

75

9-1=8
24-9=15
46-24=22
and
15-8=7
22-15=7

therefore 22+7=29 and 29+46=75

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jaga slm  (10 years ago)

Tn = n/2[2* + (n-1)7] = (7n^2 – 5n)/2
Rakesh how come there 2*??? can u explain....

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hegdeshashanka  (10 years ago)

1^2=1
3^2-0=9
5^2-1=24
7^2-3=46
9^2-5=76

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