Cheers for the help.. this is what i did:
λ₀ = λ \sqrt{}[(c-v)/(c+v)]
and because
z = (λ₀ - λ)/λ
z = \sqrt{}[(c-v)/(c+v)] - 1
But when i sub in my value for v, this gives me a negative redshift. Wouldn't this mean that the object was in fact moving towards me?
Have I done...
A distant galaxy is moving away from us at a speed of 1.85x10^7m/s. Starting from the formula for the doppler shifted frequency, derive a formula for the change in wavelength and hence calculate the fractional redshift (λ'-λ₀)/λ₀ in the light from the galaxy.
I'm pretty confused at the moment...