The area of the triangle DME is | em || MD |

/2 = x 1(| y 1 |+k/x 1)

/2,

The area of the triangle CMF is | FM || MC |

/2 = | y 1 |(x 1+k/| y 1 |)

/2

Obviously equal, so the areas of △CEF and △DEF are equal.

The slope of the straight line EF is -y 1/x 1, and the slope of the straight line CD is (k/x1-y1)/(x1-k/y1) =-y/.

The straight line EF is parallel to the straight line CD,

So △AOB is similar to △FOE.