The total mass of a binary system can be calculated from a. ...

[Yolanda]

The total mass of a binary system can be calculated from
 
  a. the ratio of the angular separation from the center of mass of each of the stars.
  b. the distance to the binary and its radial velocity.
  c. the semimajor axis and period of the orbit.
  d. the radial velocities of the two stars.
  e. the time required for the smaller star to eclipse the larger star.

Question 2

The primary mirrors of most radio telescopes is similar to the primary mirror of a reflecting optical telescope in that
 
  a. they are both concave in shape.
  b. they are both convex in shape.
  c. they are typically the same size.
  d. they are both made of metal.
  e. they have nothing in common.

[Moriaki]

Answer to Question 1

c

Answer to Question 2

a

[Yolanda]

Thank you!

[Moriaki]

Always glad to help...