Câu hỏi 26
Tính
$$\begin{aligned}&(1-\frac12-\frac13-\cdots-\frac1{2011})(\frac12+\frac13+\cdots+\frac1{2011}+\frac1{2012})\\&\quad -(1-\frac12-\frac13-\cdots-\frac1{2011}-\frac1{2012})(\frac12+\frac13+\cdots+\frac1{2011}).\end{aligned}$$
$$\begin{aligned}&(1-\frac12-\frac13-\cdots-\frac1{2011})(\frac12+\frac13+\cdots+\frac1{2011}+\frac1{2012})\\&\quad -(1-\frac12-\frac13-\cdots-\frac1{2011}-\frac1{2012})(\frac12+\frac13+\cdots+\frac1{2011}).\end{aligned}$$