# How to derive the equation for the age of a flat universe with a positive cosmological term?

Can anyone show the steps involved in deriving this equation from the friedmann equation with the cosmological constant involved

• It would help if you (a) used Mathjax for the maths, (b) explained where you got the expression (e.g. link to paper) and (c) explained the symbols (what in this case are $H_D, t_D, \Omega_{\Lambda} and \Omega_m$. Also try searching Physics SE where similar questions appear. Thanks. Jun 6 '18 at 18:37
• Please also show what you have done to obtain the solution yourself. The steps should involve 1) neglect everything but matter and dark energy from the Friedmann equation, 2) integrate the equation over time, 3) approximate $a(t)$ at late times ("late" meaning after matter-$\Lambda$ equality), and 4) isolate $t_0$
– pela
Jun 7 '18 at 9:17