Answer:
 1 / f = 1 / p + 1 / q
Explanation:
For this exercise we will use two methods, an analytical method which is to use the constructor equation
         1 / f = 1 / p + 1 / q
where f is the focal length, positive for converging lenses and negative for diverging lenses, p and q are the distance to the object and the image respectively
         m = h’/ h = - q / p
where m is the magnification, h ’and h are the height of the image and the object.
We will also use a graphical method, where three rays will be traded
1) A ray that passes through the center of the lens and should not
2) a ray that passes through the focal length and comes out parallel to the lens
3) A ray that is horizontal and comes out through the focal from the other side
for this second method see the attachment
