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If the number of terms in the expansion...

If the number of terms in the expansion `(1+2x-3y+4z)^(n)` is `286`, then find the coefficient of term containing `xyz`.

Text Solution

Verified by Experts

The correct Answer is:
`-17280`

Number of term in the expansion
`= .^(n+4-1)C_(4-1) = .^(n+3)C_(3) = ((n+3)(n+2)(n+1))/(3!)`
According to the question,
`((n+3)(n+2)(n+1))/(3!) = 286`
`:. n = 10`
So, the term containing `(xyz)` is `(10!)/(7!!!!!!!!) (1)^(7) (2x)^(1) (-3y)^(1)(4z)^(1)`
`= -17280 xyz`.
Therefore, the required coefficient is `- 17280`.
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