a=(2x² - 5x +4)(2x² - 5x + 8
) + 4 reprezinta patratul perfect al numarului (2x²-5x+6)²,oricare ar fi x∈N
(2x² - 5x +4)(2x² - 5x + 8
) + 4=
=(2x² - 5x +4)(2x² - 5x + 4+4
) + 4=
=(2x² - 5x +4)(2x² - 5x + 4) +4(2x² - 5x +4) + 4=
=(2x² - 5x +4+2)²=
=(2x² - 5x +6)²