therefore

The slope of L2 is-1/p.

2. According to all p (1, 4), find L 1.

Linear equation of L2

3. Bring the focus of X axis and L 1 into the equation of L 1.

The coordinates of point a are denoted by p.

4, the same as 3

The coordinates of point b are denoted by p.

5. Use AB two points to find the coordinate equation of AB midpoint.