1.

Find the term independent of `x` in the expansion of `(3x - (2)/(x^(2)))^(15)`.

Answer» Given expansion is `(3x - (2)/(x^(2)))^(15)`
Let `T_(r + 1)` is the general term.
`:. T_(r + 1) = .^(15)C_(r) (3x)^(15 - r) ((-2)/(x^(2)))^(r) = .^(15)C_(r) (3x)^(15 - r) (- 2)^(r) x^(-2r)`
`= .^(15)C_(r) 3^(15 - r) x^(15 - 3r) (-2)^(r)`
For independent of x, `15 - 3r = 0 rArr r = 5`
Since, `T_(5 + 1) = T_(6)` is independent of x.
`T_(5 + 1) = .^(15)C_(r) 3^(15 - 5) (-2)^(5)`
`= - (15 xx 14 xx 13 xx 12 xx 11 xx 10 !)/(5 xx 4 xx 3 xx 2 xx 1 xx 10 !) . 3^(10).2^(5)`
`= -3003.3^(10). 2^(5)`


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