1. Thực hiện phép tính (bằng cách thích hợp nếu có thể):
a. $\left ( \frac{-1}{2} \right )^{2}-1\frac{4}{5} : \left ( 2^{3}-\frac{4}{5} \right )$
b. $\frac{14}{11}.\frac{-7}{13}+1\frac{3}{39}+\frac{-7}{11}.\frac{8}{13}$
c. $12\frac{4}{5}:\left ( -\frac{7}{3} \right )-15\frac{4}{5}:\left ( -\frac{7}{3} \right )+\sqrt{\frac{25}{49}}$
Bài Làm:
a. $\left ( \frac{-1}{2} \right )^{2}-1\frac{4}{5} : \left ( 2^{3}-\frac{4}{5} \right )$
= $\frac{1}{4}-\frac{9}{5}:(8-\frac{4}{5})$
= $\frac{1}{4}-\frac{9}{5}:\frac{36}{5}$
= $\frac{1}{4}-\frac{9}{5}.\frac{5}{36}$
= $\frac{1}{4}-\frac{1}{4}$
= 0
b. $\frac{14}{11}.\frac{-7}{13}+1\frac{3}{39}+\frac{-7}{11}.\frac{8}{13}$
= $\left ( \frac{14}{11}.\frac{-7}{13}+\frac{-7}{11}.\frac{8}{13} \right )+1\frac{1}{13}$
= $\frac{14.(-7)+(-7).8}{11.13}+\frac{14}{13}$
= $\frac{22.(-7)}{11.13}+\frac{14}{13}$
= $\frac{-14}{13}+\frac{14}{13}$
= 0
c. $12\frac{4}{5}:\left ( -\frac{7}{3} \right )-15\frac{4}{5}:\left ( -\frac{7}{3} \right )+\sqrt{\frac{25}{49}}$
= $12\frac{4}{5}.\left ( -\frac{3}{7} \right )-15\frac{4}{5}.\left ( -\frac{3}{7} \right )+\frac{5}{7}$
= $\left ( 12\frac{4}{5}-15\frac{4}{5} \right ).\frac{-3}{7}+\frac{5}{7}$
= $3.\frac{3}{7}+\frac{5}{7}$
= $\frac{14}{7}$
= 2