use discriminant (delta)

Does not intersect with x axis = no real roots = delta < 0 b² - 4ac =(2m)² - 4(-1)(-2m²-9) = 4m² - 8m² - 36 = -4m² - 36 For any real number m, m² >= 0, so -4m² <= 0. Thus, -4m² - 36 < 0 for any real number m.

判别式小于0