The eigenvalue method for cross t-intersecting families

We show that the Erd?s–Ko–Rado inequality for t-intersecting families of k-element subsets of an n-element set can be easily extended to an inequality for cross t-intersecting families by using the eigenvalue method if n is relatively large depending on k and t. The same method applies to the case of t-intersecting families of k-dimensional subspaces of an n-dimensional vector space over a finite field.