Rewrite as .

Let . Substitute for all occurrences of .

Consider the form . Find a pair of integers whose product is and whose sum is . In this case, whose product is and whose sum is .

Write the factored form using these integers.

Replace all occurrences of with .

Rewrite as .

Since both terms are perfect squares, factor using the difference of squares formula, where and .

Rewrite as .

Since both terms are perfect squares, factor using the difference of squares formula, where and .

Remove unnecessary parentheses.

Factor x^4-40x^2+144