The question is:
P is any point on the hyperbola with the equation . S is the focus and S' is the focus , where e is the eccentricity. Show that
I've found the length ofSP and S'P using good old Pythagoras
and similarly , which gives me
If one of the signs changes in SP or S'P then I'd get the right answer. Can someone please check if I made a mistake with the signs? Thanks.