Câu 26:
lim[11.2+12.3+...+1n(n+1)]\lim \left[ {\dfrac{1}{{1.2}} + \dfrac{1}{{2.3}} + ... + \dfrac{1}{{n\left( {n + 1} \right)}}} \right]lim[1.21+2.31+...+n(n+1)1] bằng:
