When the squared term is negative, the parabola opens:

1. Orientation flips with the sign of the leading term. 2. When the squared term is positive, the parabola opens upward. 3. When the squared term is negative, the parabola opens downward. 4. So the sign alone decides which way the curve turns. _Source: OpenStax Elementary Algebra 2e (CC BY 4.0), Ch 10 'Quadratic Equations', sections 10.1-10.5_