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.