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7.Binomial Theorem
easy
The middle term in the expansion of ${\left( {x + \frac{1}{{2x}}} \right)^{2n}}$, is
A
$\frac{{1.3.5....(2n - 3)}}{{n!}}$
B
$\frac{{1.3.5....(2n - 1)}}{{n!}}$
C
$\frac{{1.3.5....(2n + 1)}}{{n!}}$
D
None of these
Solution
(b) Obviously the middle term $ = {\,^{2n}}{C_n}{(x)^n}.{\left( {\frac{1}{{2x}}} \right)^n}$
$ = \frac{{2n!}}{{n!.n!{{.2}^n}}} = \frac{{1.3.5….(2n – 1)}}{{n!}}$.
Standard 11
Mathematics