Solution: Let $ u = x^2 $, so the expression becomes $ u^2 - 13u + 36 $. Factor: $ (u - 9)(u - 4) $. Substitute back: $ (x^2 - 9)(x^2 - 4) $. Each is a difference of squares: $ (x - 3)(x + 3)(x - 2)( - Portal da Acústica