The implicit equation 



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(<i>x</i><sup>2</sup> + 2<i>ay</i> &#8722;<i>a</i><sup>2</sup>)<sup>2</sup> = <i>y</i><sup>2</sup>(<i>a</i><sup>2</sup> &#8722; <i>x</i><sup>2</sup>)</td></tr></table>
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represents a family of functions the members of
the family corresponding to different values of
<i>a</i>.
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Re-arrange the equation into the form <i>y</i> = <i>f</i>(<i>x</i>)
and draw some graphs belonging to the family for
different values of <i>a</i>. What is the domain of
the function <i>f</i>(<i>x</i>)?