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