Your method: draw a sketch first, because the coefficient of quadratic term is (-1) and-1 is negative, so the secondary image opens downward. Symmetry axis formula (-b divided by 2a), in this question, A is-1 and B is 2, so the symmetry axis is a straight line x= 1. When x is from 1 to positive infinity, the image decreases, and the point where the symmetry axis intersects the image is the maximum value of the whole image. So, one problem: the maximum value 1 has no minimum value. Two questions: the maximum value is 0 and the minimum value is -3. Three questions: the maximum value is 0 and the minimum value is -3. Four questions: the maximum value 1.