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Question

5+9+13+.......upto n. termsIf 7+9+11+..... upto (n+1) terms=1716 then n is equal to


A
7
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B
6
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C
9
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D
none of these
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Solution

The correct option is A 7

5+9+13+..... n terms 7+9+.....to (n+1) terms=1716

n2[10+(n1)4]n+12[14+n2]=1716

n[4n+6](n+1)(n+7)=1716

n[4n+6](n+1)(2n+14)=1716

n(2n+3)(n+1)(n+7)=1716

32n2+48n=17(n2+8n+7)

15n2+48n136n119=0

15n288n119=0

15n2105n+17n119=0

15n(n7)+17(n7)=0

n=7


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