Afocal arrangement that has a secondary mirror that reflects the focused light back through a hole in the primary mirror is a
a. cassegrain focus
b. newtonian focus
c. schmidt-cassegrain focus
d. schmidt focus

a. Cassegrain focus is the focal arrangement in a Cassegrain reflector used in optical telescopes and radio antennas. The primary mirror is a concave mirror, and the secondary mirror that reflects the focused light back to it is a convex mirror.

Because the earth is not round ,but it may seem round when viewed from ,our planet but true some points earth is not round was an oblate spheroid -a square that it squashed as globe however is not even a perfect oblate spheroid.in fact isaac newton's first proposed that earth was not perfectly round but it was an oblate spheroid instead.that mean a square that is squashed as its poles and swollen at the