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Find the 4th term from the end in the expansion of (\frac{3}{x^{2}}-\frac{x^{3}}{6})^{7}

 

  • Option 1)

    -\frac{35}{48}x^{6}

  • Option 2)

    \frac{35}{24}x^{6}

  • Option 3)

    -\frac{35}{24} x^{6}

  • Option 4)

    \frac{35}{48} x^{6}

 

Answers (1)

best_answer

As learnt in concept

General Term in the expansion of (x+a)^n -

T_{r+1}= ^{n}c_{r}\cdot x^{n-r}\cdot a^{r}
 

- wherein

Where r\geqslant 0 \, and \, r\leqslant n

r= 0,1,2,----n

 

 T_{4 \: \: fromlast}= ^tC_3 (\frac{-x^{3}}{6})^{4}(\frac{3}{x^{2}})^{3}

=\frac{7!}{4!3!}+\frac{x^{12}}{6^{4}}*\frac{3^{3}}{x^{6}}

=\frac{35}{48}x^{6}

 


Option 1)

-\frac{35}{48}x^{6}

Incorrect option

Option 2)

\frac{35}{24}x^{6}

Incorrect option

Option 3)

-\frac{35}{24} x^{6}

Incorrect option

Option 4)

\frac{35}{48} x^{6}

correct option

Posted by

prateek

View full answer

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