If $x,\;y$ and $r$ are positive integers, then $^x{C_r}{ + ^x}{C_{r - 1}}^y{C_1}{ + ^x}{C_{r - 2}}^y{C_2} + .......{ + ^y}{C_r} = $
If $x,\;y$ and $r$ are positive integers, then $^x{C_r}{ + ^x}{C_{r - 1}}^y{C_1}{ + ^x}{C_{r - 2}}^y{C_2} + .......{ + ^y}{C_r} = $
- A
$\frac{{x\;!\;y\;!}}{{r\;!}}$
- B
$\frac{{(x + y)\;!}}{{r\;!}}$
- C
$^{x + y}{C_r}$
- D
$^{xy}{C_r}$
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