7.Binomial Theorem
hard

 $(1+ x)(1- x)^{10} (1+ x + x^2 )^9$  ના વિસ્તરણમાં $x^{18}$ નો સહગુણક મેળવો.

A

$84$

B

$126$

C

$-126$

D

$-84$

(JEE MAIN-2019)

Solution

$(1+x)(1-x)^{10}\left(1+x+x^{2}\right)^{9}$

$\left(1-x^{2}\right)\left(1-x^{3}\right)^{9}$

$^{9} \mathrm{C}_{6}=84$

Standard 11
Mathematics

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