1/r = a/b2 * (1+e cosθ)
The Attempt at a Solution
How do you derive 7.27?
I tried to substitute r in the orbit equation by (acosψ - ae) / cosθ and got
(cos ψ - e)/cosθ*(1+e cosθ)=b^2/a^2 I don't know what to do next. Please help, thank you.