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动点问题是中考数学的常见题型,解题时要关注题中的不变量、特殊点及特殊位置,特别是当直线与圆、双曲线、抛物线相切时,可能取得最值,从而确定取值范围,现举几例说明.例1在平面直角坐标系x Oy中,A(-2,0)、B(0,4),圆C的圆心为C(3,0),半径为3,若D是圆C上的一个动点,线段DA与y轴交于E点,若△ABE的面积为S,则S的范围是
The problem of moving point is a common type of mathematics in senior high school entrance examination. When solving a problem, we should pay attention to the invariants, special points and special positions in the question, especially when the straight line is tangent to a circle, hyperbola or parabola. Example 1 In Cartesian coordinate system x Oy, A (-2,0), B (0,4), the center of circle C is C (3,0), the radius is 3. If D is a moving point on the circle C, the line DA and the y-axis intersect at point E. If the area of △ ABE is S, the range of S is