How to find Image of a point in a line? Best trick

Image of a Point in a Plane :

Let P and Q be two points on given plane such that 

(i)     line PQ is perpendicular to the plane and

(ii)    mid point of PQ lies on the plane

Then either of the point is the image of the point in the plane.

Algorithm For Finding the image of a point in a given Plane :

Step I: Write the equation of the line passing through P and normal to the given plane

Step II: Write the coordinates of image Q as (x1 + ar, y1 + br, z1 + cr)

Step III: Find the coordinates of the mid-point of PQ.

Step IV: Obtain the value of r by putting the coordinates of mid point in the equation of plane.

Step V: Put the value of r in the coordinates of Q.