Answer:
I'll help if you need it.
Step-by-step explanation:
 
        
             
        
        
        
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.
 
        
             
        
        
        
8
2380
=
8 goes into 80 0 times then goes into 380 47.5 times then it goes into 2000 250 times so 250 + 47.5 = 293.5
        
             
        
        
        
R+s-t-(r-s+t)
=2s-t is the answer
People think this answer would be just =2s but I have verified with an online calculator and the answer that textbooks look for regarding this is 2s-t
You would assume you would go r-r and thats 0 so no r's
you would say s-(-s) makes it plus and theres 2s
and you would say -t -(+t) is -t 
that's why the answer is 2s-t
At first I also did t-(+t) and thought it would be no t's but the answer is in fact 2s-t 
        
             
        
        
        
<span>20 hundreds is equal to 2 thousands, however 20 hundreths is not equal to 2 thousandths. 2 in the 0,2 is 100 times greater than 2 in 0,002.
</span>