PLEASE HELP- doppler shift equation question?

Question

If you use the equation Δ λ / λ0 = rv / c to calculate the velocity of a star and apply it to a galaxy or a quasar with a redshift, Δ λ / λ0, of 2, what is the value of the velocity that you get? Is this the correct velocity for this galaxy? Why or why not?

Answer 1

For cosmologically-distant objects, you first of all need to define what you mean by your mutual velocity.  Really, you're both embedded in an expanding space, and both have near-zero velocity with respect to space.  "Velocity" doesn't have the usual meaning.  In any case, your formula is only a first-order approximation.

Answer 2

You would have to use the relativistic Doppler effect equation for most observations to get good values.

If I understand your values correctly, the velocity of the observed object is 60% of the speed of light.

Somebody should please correct me, if I am now wrong:

2 = sqrt((1+v/c)/(1-v/c))