2012中考数学一轮复习【代数篇】19.二次函数（2012, mathematics exam review [algebra] 19., two function）.docVIP

2012中考数学一轮复习【代数篇】19.二次函数（2012, mathematics exam review [algebra] 19., two function） Quadratic function of the senior high school entrance examination review Knowledge point: Master the quadratic function of image and character and parabola translation rules; determine the vertex coordinates, parabolic symmetry axis and the value. Classic examples: [1] quadratic function of the image as shown in the figure, then, the four type algebra, the positive value is () A, 4 B, 3 C, 2 D, 1 Analysis: 1 dreams R 0 Answer: A Commentary: the parabola opening decision symbols, determined by the symmetry axis position of the symbol, judged by the parabola and axis intersection position symbol. Judging by the number of intersections of a parabola with the axis of the symbol, if the axis marked 1 and 1, is a combination of function values can be determined, and the symbol. [2] = 0, known to the parabolic pan down 1 units, a new parabola and left to translate 5 units from the vertex is (2, 0), and the original formula of parabola. Analysis: the original image shows that the parabolic point (1, 0) after the new parabolic right translation; 5 units, to translate 1 units is the original parabolic. Solution: analytical formula can be set for a new parabolic formula, the original parabolic, and we know that the original parabolic point (1, 0) So, solution The original formula for parabolic star: Commentary: the key to solve these problems is a profound understanding of the relationship between the two parabola before and after translation, as well as the relation between the corresponding analytic type, and pay more attention to the application of reverse thinking. In addition, can also concern the vertex of a parabola what happened to move, several common modes of change: the reverse opening (or rotating 1800), the vertex coordinates unchanged, just turn the two; parabola about axial symmetry, the axial symmetry of vertex, the number two on the reverse; parabolic symmetry axis, the verte