i have a parabolic mirror with equation x=-1/2y^2
there are 5 parallel rays coming into the parabolic mirror at y=2,y=1,y=0,y=-1,y=-2
(a) find the focal length
i found the equation f=D^2/(16c) where D is the diameter, and c is the depth.
this gives me a focal length of (1/2)
i was...