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## Homework Statement

For a κ=0 universe with no cosmological constant, show that H(z)=H

_{0}(1+z)

^{3/2}

## Homework Equations

Friedmann equation: H

^{2}=[itex]\frac{8*\pi*g}{3c^2}[/itex]-[itex]\frac{κc^2}{r^2}[/itex]*[itex]\frac{1}{a(t)^2}[/itex]

## The Attempt at a Solution

I know that R(z)=R

_{0}/(1+z) but I do not know where this comes from. Following this, I should be able to take a density ρ(z)=ρ(now)*(1+z)^3 and input it into the Friedman equation but I am not sure how to proceed