Câu hỏi 17
Tính giá trị
$$\begin{aligned}&\left(\frac12+\frac{345}{456}+\frac{567}{678}+1\right)\left(\frac{345}{456}+\frac{567}{678}+\frac78\right)\\&\quad-\left(\frac12+\frac{345}{456}+\frac{567}{678}\right)\left(\frac{345}{456}+\frac{567}{678}+\frac78+1\right).\end{aligned}$$
$$\begin{aligned}&\left(\frac12+\frac{345}{456}+\frac{567}{678}+1\right)\left(\frac{345}{456}+\frac{567}{678}+\frac78\right)\\&\quad-\left(\frac12+\frac{345}{456}+\frac{567}{678}\right)\left(\frac{345}{456}+\frac{567}{678}+\frac78+1\right).\end{aligned}$$