If the term independent of x in the expansion of 3 2 x 2 - 1 3 x 9 is k , then 18 k is equal to:

If the term independent of x in the expansion of 32x2-13x9 is k, then 18k is equal to:
  1. 11
  2. 5
  3. 9
  4. 7

Solution

Tr+1=9Cr3x229-r-13xr

=9Cr329-r-13rx18-3r

For the term independent of x, put r=6

⇒T7=9C6323-136=9C3163=9×8×73×2×1163=718

⇒k=T7⇒k=718⇒18k=7

Asked in: JEE Main 2020 (03 Sep Shift 2)

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