One assumption made in the derivation of these expressions allows for the simplification of potentially 9 equations into one. One of these expressions features the sum of the density and three times the pressure on the right hand side, while another of them contains the difference between a term proportional to the density and a term proportional to the curvature. The second of these expressions can be rewritten in terms of the critical density, depending on which their solutions are characterized as having open, flat, 
One assumption made in the derivation of these expressions allows for the simplification of potentially 9 equations into one. One of these expressions features the sum of the density and three times the pressure on the right hand side, while another of them contains the difference between a term proportional to the density and a term proportional to the curvature. The second of these expressions can be rewritten in terms of the critical density, depending on which their solutions are characterized as having open, flat, or closed geometry. These expressions give the ratio of time derivatives of the scale factor to the scale factor itself, and the second of them defines the square of the Hubble expansion parameter. Derived from the Einstein field equations by assuming homogeneity and isotropy, for 10 points, identify these cosmological equations which yield a metric named for their namesake, Robertson, and Walker.
One assumption made in the derivation of these expressions allows for the simplification of potentially 9 equations into one.
Friedmann equations [prompt on Einstein field equations before "density"]