I'm studying from the Dodelson book on Cosmology and I got stuck on a specific derivation. In this derivation I need to compute $$\frac{d}{dy}\left(\frac{1}{ayH}\right).$$ Here $y= \frac{a}{a_\text{eq}}$, a parameter. The book says that $$\frac{d}{dy}\left(\frac{1}{ayH}\right) = -(1+y)^{-1}(2ayH)^{-1},$$ but to me this doesn't make sense at all. I've tried writing everything out, but I never seem to get this result.



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