Let find Lᵖ(Rᵈ) where p>1. Let also (1)/(p)+(1)/(q)=1. Show that ||f||_(p)=sup| int fg|:||g||_(q)=1. Hint: One side of the inequality, use Hölder inequality. For the other side of the inequality, use the fact that the supremum is always greater than or equal to the integral.