|Jul21-12, 04:40 AM||#1|
problem about calculating focal length of a telescope
I am preparing an exam about optics and I can't understand a formula.
my problem is at the end of the second page (the explanation is in Italian, but the formulas are easy to read for everybody).
I can't understand how in the last step
f=R/2 - (1+b) * r^2/4R etc they found -(1+b)
can somebody help me please?
|Jul22-12, 07:19 PM||#2|
Are you asking how they mathematically got from the previous equation to the last one?
|Jul23-12, 01:43 AM||#3|
yes. I understand what is substituted in what, but I get a different sign in the second term, and I'd like to see all the passages...
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