Вот пример использования Linq Intersect.
// Assign two arrays.
int[] array1 = { 1, 2, 4 };
int[] array2 = { 2, 3, 4 };
// Call Intersect extension method.
var intersect = array1.Intersect(array2);
foreach (int value in intersect)
{
label1.Text += value + "\n";
}