on the last page of t2_InClass_problems.pdf, consider problem #44
Work this problem the standard way.

Now work the same problem via Gauss.
We derived in class (gauss2.m) that the focal point on the left (F1) is
(f1(f2-d))/(f1+f2-d)
to the left of lens f1, and the focal point on the right (F2) is
(f2(f1-d))/(f1+f2-d)
to the right of lens f2, and that the combined focal length was:
f=f1 f2/(-d + f1 + f2)
and that the magnification was 
-f/x
where x was measured as distance away from F1 and y away from F2 and
x y =f^2

Once you have F1 & F2 determined you should be immediately 
be able to find /image/object locations via Gauss.
If the object is actually 14 cm away from the f1 lens, where is the image?

IF the object remains 14 cm from f1, but the separation, d, between f1 & f2 is 
reduced to 20 cm, where is the image? what is its magnification?
Work this problem both ways.

Remark: If you look at the Galilean telescope (34-100) and the usual
telescope you'll see that f1+f2=d, which puts zeros in the denominator of
all of the above expression, so more care would be required there.

34-101 (d)
Note that the formula that they would have you derive in parts (a)-(c)
is the Gauss result disguised by writing |f2| for -f2.

34-51
34-53