The coefficient of t 4 in the expansion of 1 - t 6 1 - t 3 is

The coefficient of t4 in the expansion of 1-t61-t3 is
  1. 10
  2. 14
  3. 15
  4. 12

Solution

1-t61-t3=1-t631-t-3

=1-t18-3t6+3t12 1-t-3

∴ Co-efficient of t4=1× 3+4-1C4= 6C4=15

Asked in: JEE Main 2019 (09 Jan Shift 2)

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