# One of the foci of the rectangular hyperbola $xy=18$ is

$\begin{array}{1 1}(1)(6 , 6)&(2)(3 , 3)\\(3)(4 , 4)&(4)(5 , 5)\end {array}$

The equation of the rectangular hyperbola is $xy=18$
$c^2=18 => \large\frac{a^2}{2}$$=18$
$a^2=36 => a= 6$
=>$(6 , 6)$
Hence 1 is the correct answer.