![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/c8ea15ce36d3d539cd11e6723987e950352ab057?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
解:如图1,(1)当BC∥DA,BC=DA时,
当点D在A的左边时,由点C平移到点A是横坐标减3,纵坐标减1,
那么由点B平移到点D也应如此移动:2-3=-1,1-1=0,故此时D的坐标(-1,0);
当D在A右边时,由点B平移到点A是横坐标减1,纵坐标加1,
那么由点C平移到点D也应如此移动:4-1=3,3+1=4,故此时D的坐标(3,4);
当AC∥DB,AC=BD时由点A平移到点C是横坐标加3,纵坐标加1,
那么由点B平移到点D也应如此移动:2+3=5,1+1=2,
故此时D点坐标为(5,2)
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/a8ec8a13632762d0ba074d0ea3ec08fa513dc642?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
所以D点坐标为(-1,0)或(3,4)或(5,2).
(2)如图2,由点A(1,2),B(2,1),可知直线AB的斜率为-1,AB=
,
∵EF∥AB,且EF=
,
∴OE=1,OF=1,
∴E的坐标为(1,0),F的坐标(0,1),或E(-1,0),F(0,-1);