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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