设A(x1,y1),B(x2,y2).代入椭圆方程得：
(x1)²/4+（y1）²=1,(x2)²/4+（y2）²=1作差
(x1-x2)(x1+x2)/4+(y1-y2)(y1+y2)=0.
∵x1+x2=2,y1+y2=1,设(y1-y2)/(x1-x2)=k,
∴(2/4)+k=0,
∴k=-1/2.
根据点斜式方程,得：x+2y-2=0.