“存在性”问题是探索性问题的重要形式 ,它要求学生紧扣题设条件 ,把握特征 ,拔开迷雾 ,对“是否存在”作出准确判定并进行正确的推理。解这类题一般遵循“三部曲”,即假设存在——演绎推理——得出结论 (合理或矛盾两种情形 )。下面试举几例予以说明 :例 1.已知 :抛物线y =ax The question of “existence” is an important form of the exploratory problem. It requires students to closely follow the conditions of the title, grasp the characteristics, pull out the fog, make an accurate judgment on “whether it exists,” and conduct correct reasoning. Solutions to such questions generally follow the “trilogy”, that is, assuming existence - deductive reasoning - to draw conclusions (reasonable or contradictory situations). Here are a few examples to illustrate: Example 1. Known: Parabola y = ax