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The number of terms independent of $x$ in the binomial expansion of $\left(3x^2 + \dfrac{1}{x}\right)^{10}$ is 

  1. $0$
  2. $1$
  3. $2$
  4. $5$
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(x+y)^{n}={n \choose 0}x^{n}y^{0}+{n \choose 1}x^{n-1}y^{1}+{n \choose 2}x^{n-2}y^{2}+\cdots +{n \choose n-1}x^{1}y^{n-1}+{n \choose n}x^{0}y^{n},

let mth  term is independent of x (here m is integer)

(3x2)m x ($\frac{1}{x}$)10-m

x2m-10+m

2m-10+m=0

m=10/3 not integer

Anser  : A

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