y = x² + tx + t + 3= x² + tx + t²/4 -t²/4 + t + 3= (x + t/2)² -t²/4 + t + 3 要使y = x² + tx + t - 3恒大于0,则-t²/4 + t + 3 > 0即可t² - 4t - 12 < 0(t - 6)(t...