You need to save the Array returned by the intersect method into a variable and then print that. Also, the intersect operation is really only useful with two different arrays.

For example:

// ... setup numbers with 1..7
Array otherNumbers = new Array(3);
otherNumbers.insert(1);
otherNumbers.insert(5);
otherNumbers.insert(10);
Array intersection = numbers.intersect(otherNumbers);
intersection.print(); // should have 1 and 5