1.

In \((3x^2-\frac{1}{x})^{18}\)which term contains x12?

Answer»

The general term of the expression is 

Tr + 1 = 18Cr (3x2 )18 – r \((\frac{-1}{x})^{r}\) 

= 18Cr (-1)r 318-r x 36-3r

For coefficient of x12   36 – 3r = 12

 ∴ r = 8

∴ T8 = 18C8 (-1)8 318-8 x36-24

= 18C8310

9 term contains x12 and coefficient is 18C8310



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