I don't understand the first conclusion of the user Tomas in the exercise
Why does the inequality $$\int_{\mathbb{R}} (1+x^2)^{-\alpha q/2}(\log (2+x^2))^{-q}\ge \int_{\mathbb{R}}(1+x^2)^{-\alpha q/2}(2+x^2)^{-qt}. $$
lead us to conclude that if $q\in [1,1/\alpha)$ then $f\notin L^q(\mathbb{R})$?
Thanks