Chapter 8.7 Planetary Motion  Kepler's Problem



                   (l/r^2)dr
θ(r) = ∫──────────────── + constant
          √2μ[E +（k/r）-（l^2/2μr^2)]


Change variable by using u≡l/r and integral it,

I have a problem when evaluating at last term,

the following is the answer in the book:


" We can choose the point from which θ is measured so that the constant

 is -π/2 "

                     (-l^2/μk)u + 1        -αu + 1
sin (θ+constant) = ────────── = ─────
                    √1+ 2El^2/μk^2          ε


where α= l^2/μk    ε= √1+2El^2/μk^2

問題是 要怎麼知道-π/2 這個值呢？

最後答案是

α/r = 1 + εcosθ

感謝您的回答<(_ _)>

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