Giải câu 1 trang 50 sách phát triển năng lực toán 7 tập 1

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