则这条弦所在的直线方程是____________．2答案2x＋4y－3＝0解析设弦的两个端点为Ax1，y1，Bx2，y2，则x1＋x2＝1，y1＋y2＝1x2x2122∵A，B在椭圆上，∴＋y21＝1，＋y2＝122x1＋x2x1－x2＋y1＋y2y1－y2＝0，2即y1－y2x1＋x21＝－＝－，2x1－x22y1＋y2
1即直线AB的斜率为－2111x－，∴直线AB的方程为y－＝－222即2x＋4y－3＝0考点二例2圆锥曲线中的定值、定点问题
x2y21已知椭圆C：2＋2＝1经过点0，3，离心率为，直线l经过椭圆C的右焦点Fab2交椭圆于A、B两点，点A、F、B在直线x＝4上的射影依次为D、K、E1求椭圆C的方程；→→→→2若直线l交y轴于点M，且MA＝λAF，MB＝μBF，当直线l的倾斜角变化时，探求λ＋μ的值是否为定值？若是，求出λ＋μ的值；否则，说明理由；3连接AE、BD，试探索当直线l的倾斜角变化时，直线AE与BD是否相交于定点？若是，请求出定点的坐标，并给予证明；否则，说明理由．1待定系数法；2用直线的斜率为参数建立直线方程，代入椭圆方程消y后
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