Judging the open direction of quadratic function has nothing to do with B and C, but only looks at A (which can be understood as the coefficient of quadratic term). The general form of quadratic function is y = ax? +bx+c, if the quadratic coefficient is a >；; 0, the opening is upward, otherwise, the opening is downward. Let's analyze the four formulas you gave (a>0 is the premise). In the first formula, the quadratic coefficient A is greater than 0, so the opening is upward. In the second formula, the quadratic coefficient -a