The (1) point is symmetrical about a straight line.

The method of solving equations,

Let the point where P is symmetrical about the straight line L be P'

Then the midpoint of PP' is on a straight line, and an equation is obtained.

The slope of PP' and the slope of L are negative reciprocal (two straight lines are perpendicular), and another equation is obtained.

Only the following equations need to be solved

(2) The straight line is symmetrical about the point.

The undetermined coefficient method can solve the equation.

Let the straight line l be L' and be symmetrical about p.

Then l' is parallel to l,

Let's set the equation of l', and then use the distance from p to two straight lines to get the parameters, and get the straight line equation.