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JEE Advanced · Mathematics · 16. Limits

For aR, a>1, let limn1+23++n3n7/31an+12+1an+22++1an+n2=54. Then the possible value(s) of a is/are:

  1. A 8
  2. B -9
  3. C -6
  4. D 7
Verified Solution

Answer & Solution

Correct Answer

(B) -9

Step-by-step Solution

Detailed explanation

Let S=limn1+213+313++n13n731an+12++1an+n2
S=limnr=1nr13n73r=1n1na+r2
S=limnr=1nrn131n×n13n73r=1n1a+rn21n2
S=limnr=1nrn13.1nr=1n1a+rn21n
S=01x13dx011a+x2.dx
S=x434301-1x+a01
S=341a-1a+1=54
1aa+1=172
a2+a-72=0
a=8 or a=-9
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