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7.Binomial Theorem
normal
The greatest value of the term independent of $x$ in the expansion of ${\left( {x\sin \theta + \frac{{\cos \theta }}{x}} \right)^{10}}$ is
A
$^{10}C_5$
B
$2^5$
C
$2^5 · ^{10}C_5$
D
$\frac{{^{10}{C_5}}}{{{2^5}}}$
Solution
${\left( {x\sin \theta + \frac{{\cos \theta }}{x}} \right)^{10}}$ ;$ T_{r + 1} = ^{10}C_r(x sin \theta )^{10 – r} ·{\left( {\frac{{\cos x}}{x}} \right)^r} = ^{10}C_r (sin \theta )^{10 – r} · x^{10 – 2r} (cos\theta )^r$
hence for independent of $x, r = 5$
$T_6 = ^{10}C_5 (sin \theta )^5 · (cos\theta )^5$.
$=\frac{{^{10}{C_5}{{(\sin 2\theta )}^5}}}{{{2^5}}}$
Standard 11
Mathematics