Q43 / 90 · JEE Main 2021 (01 Sep Shift 2) · Mathematics

Let Jn,m=∫01/2xnxm-1dx,∀n>m and n, m∈N. Consider a matrix A=aij3×3 where aij=J6+i,3-Ji+3,3,  i≤j0,  i>j. Then adjA-1 is :

  • A
    (15)2×234
  • B
    (15)2×242
  • C
    (105)2×236
  • Correct answer
    D
    (105)2×238

Solution

∵A=a11a12a130a22a2300a33⇒A=a11a22a33

⇒|A|=J7,3-J4,3·J8,3-J5,3·J9,3-J6,3

=∫01/2x7-x4x3-1dx·∫01/2x8-x5x3-1dx·∫01/2x9-x6x3-1dx

=∫01/2x4dx·∫01/2x5dx·∫01/2x6dx

=1(210)·(2)18

Now

adjA-1=A-12=1|A|2=(210)·2182=(105)2·(2)38

Hence, the correct answer is option: 'D'.

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