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有一座抛物线形拱桥,在正常水位时水面AB的宽为20米,如果水位上升3米,则水面CD的宽是10米,建立如图平面直角坐标系,求此抛物线的解析式。A x y B C D O5方法一:设如图抛物线的表达式为y=ax2,由题意可设B点的坐标为(10,m),D点的坐标为(5,m+3),把B、D两点的坐标代入解析式得:
There is a parabolic arch bridge, the water surface at normal water level AB width of 20 meters, if the water level rise of 3 meters, the water surface CD is 10 meters wide, the establishment of the plane rectangular coordinate system as shown in Figure parabolic equation. A xy BCD O5 Method One: Set the parabola as shown in the expression y = ax2, the coordinates of point B can be set as (10, m) and the coordinates of point D as (5, m + 3) , D coordinates of two points into the analytical formula was: