look at figure attachd
a shadow will be formd if atleast some light escapes out, i.e
frm fig.
r<c
i.e sin r<sinc
R/
900+R^2<1/1.4
simplify n u get R<30.6
and the length of shadow cn be found usin trigonometry
radius of ring on wall=x
were
[x/
10000+x^2]/
R/900+R^2 =1.4
Moderation Team
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