设M(X1,Y1) N(X2,Y2) 中点A(-1/2 ,Y0)因为M.N都在椭圆上,所以有
X1^2 +Y1^2 /9 =1 X2^2 +Y2^2 /9 =1 联立得
-9(X1+X2)/(Y1+Y2) =(Y1-Y2)/(X1-X2) 因为X1+X2=1 (Y1-Y2)/(X1-X2)=K
所以 K=-9/(Y1+Y2)
因为Y1+Y2=...
设M(X1,Y1) N(X2,Y2) 中点A(-1/2 ,Y0)因为M.N都在椭圆上,所以有
X1^2 +Y1^2 /9 =1 X2^2 +Y2^2 /9 =1 联立得
-9(X1+X2)/(Y1+Y2) =(Y1-Y2)/(X1-X2) 因为X1+X2=1 (Y1-Y2)/(X1-X2)=K
所以 K=-9/(Y1+Y2)
因为Y1+Y2=...