B
将正方形ABCD沿AB向下翻折到对角面ABC 1D 1内成为正方形ABC 2D 2,在矩形C 1D 1D 2C 2中连接D 1C 2,与AB的交点即为所求最小值点E,此时D 1E+CE=D 1C 2.因为对角线BC 1=2,C 1C 2=3,故D 1C 2=
=
=
.
B
将正方形ABCD沿AB向下翻折到对角面ABC 1D 1内成为正方形ABC 2D 2,在矩形C 1D 1D 2C 2中连接D 1C 2,与AB的交点即为所求最小值点E,此时D 1E+CE=D 1C 2.因为对角线BC 1=2,C 1C 2=3,故D 1C 2=
=
=
.