Answer:
Optical axis
Step-by-step explanation:
Optical axis is the rotational symmetry axis of the surfaces.
A line with a certain degree of rotational symmetry is called as the optical axis in an optical system.
It is the straight line that passes through the geometric center of the lens and joins two curvature centers of its surfaces.
It is also called as the principal axis.
 
        
             
        
        
        
Answer:
it will be 1/2
Step-by-step explanation:
because x×y={(6,2), (6, 8),(9,2), (9, 8)}
 
        
             
        
        
        
Divide both sides by -3, and replace  with
 with  . Then
. Then

Factorize the quadratic in  to get
 to get

which in turn means

But  for all real
 for all real  , so we can ignore the first solution. This leaves us with
, so we can ignore the first solution. This leaves us with

If we allow for any complex solution, then we can continue with the solution we ignored:
