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With some simple trigonometry one can obtain
Rr = w^2 w / tan^2tan(c * u)
which means that
R = sqrt(Rr^2 + w^2/4)
...
...
With some simple trigonometry one can obtain
Rr = w^2 w / tan^2tan(c * u)
which means that
R = sqrt(Rr^2 + w^2/4)
...