- Home
- Standard 11
- Mathematics
જો $\left( {\begin{array}{*{20}{c}}
{2n} \\
3
\end{array}} \right)\,\,:\,\,\left( {\begin{array}{*{20}{c}}
n \\
2
\end{array}} \right)\, = \,44\,:3$ અને $\left( {_r^n} \right) = 15$ હોય, તો $\,r\,\, = . .. . . $ થશે
$3$
$4$
$5$
$6$
Solution
$\left( {\begin{array}{*{20}{c}}
{2n} \\
3
\end{array}} \right)\,\,:\,\,\left( {\begin{array}{*{20}{c}}
n \\
2
\end{array}} \right)\, = \,44\,:3$
$\frac{{(2n)\,!}}{{3\,!\,(2n – 3)\,!}}.\,\frac{{2\,!(n – 2)\,!}}{{n\,!}} = \frac{{44}}{3}\,\,\,$
$\frac{{2n.(2n – 1)(2n – 2)(2n – 3)\,!}}{{3 \times 2(2n – 3)\,!}}.\frac{{2\,!(n – 2)\,!}}{{n(n – 1)(n – 2)\,!}} = \frac{{44}}{3}\,\,\,$
$\frac{{4(2n – 1)}}{3} = \frac{{44}}{3}\,\,$
$2n – 1 = 11$
$n = = 6$
$\left( {\begin{array}{*{20}{c}}
n \\
r
\end{array}} \right)\, = \,\left( {\begin{array}{*{20}{c}}
6 \\
r
\end{array}} \right) = 15\,$ પણ $\left( {\begin{array}{*{20}{c}}
6 \\
2
\end{array}} \right)\, = \,\left( {\begin{array}{*{20}{c}}
6 \\
4
\end{array}} \right) = 15$
$r = 2$ કે $r = 4$ અહીં, $r = 4$ આપેલ છે