Given $f_n(x)=(n+1)x^n; x\in [0,1]$
I want to show $\int_{[0,1]}f<\liminf\int_{[0,1]}f_n$, where $f_n$ converges pointwise to $f$ almost everywhere on $[0,1]$.
I have found that $\liminf\int f_n = \int f +\liminf\int|f-f_n|$, but I'm not sure how to use this, and I don't even know what $f_n$ converges to here. Can someone hint me in the right direction?