1. The problem statement, all variables and given/known data Starting with the equation below, I need to: - Show that there is a range of values for a for which Ωm≈1 - Derive expressions for the values of a at the endpoints of this range. 2. Relevant equations Ωm(a) = Ωm0/[Ωm0+Ωr0/a+Ωv0a3]. (0 signifies present day values, m=matter, r=radiation, v=vacuum) 3. The attempt at a solution Just setting Ωm=1 leads to a4 = -Ωr0/Ωv0, which gives imaginary values for a, which is obviously not right. However, I can't see any other way of solving this problem to get real values... Thanks in advance, Ryan.