Display a post from one of several cats with get_posts?

Hi all,

I am using the following to display the single latest post from a category.

<?php global $post;
$args = array( 'numberposts' => 1, 'category' => 7 );
$myposts = get_posts( $args );
foreach($myposts as $post) :
setup_postdata($post);
?>
Various bits of the posts and so on.

This works great, but now I want to display the single latest post from several categories. I thought I could specify a range of categories like this $args = array( 'numberposts' => 1, 'category' => 7, 8, 9 ); but when I try it, it only displays the most recent post from the first category number I enter.

Is there a way I can specify several categories here?

Many thanks!
Tim