If f is a function such that f∈L∞∩Lp0 where L∞ is the space of essentially bounded functions and 0<p0<∞. Show that ||f||Lp→||f||L∞ as p→∞. Where ||f||L∞ is the least M∈R such that |f(x)|≤M for almost every x∈X.
The hint says to use the monotone convergence theorem, but i can't even see any pointwise convergence of functions.
Any help is appreciated.
Answer
Hint: Let M<‖ and consider
\int_{E_M}\left|\frac{f(x)}{M}\right|^p\,\mathrm{d}x
where E_M=\{x:|f(x)|\gt M\}. I believe the Monotone Convergence Theorem works here.
Further Hint: M\lt\|f\|_{L^\infty} implies E_M has positive measure. On E_M, \left|\frac{f(x)}{M}\right|^p tends to \infty pointwise. MCT says that for some p, the integral above exceeds 1.
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