Giải bài 2 trang 25 toán 7 tập 1 cánh diều

a. $\left ( \frac{4}{5} - 1 \right ):\frac{3}{5}-\frac{2}{3}.0,5$

$=\frac{-1}{5}. \frac{5}{3}-\frac{2}{3}.\frac{1}{2}$

$= \frac{-1}{3} -\frac{1}{3}$

$=\frac{-2}{3}$

b. $1 - \left ( \frac{5}{9}-\frac{2}{3} \right )^{2}:\frac{4}{27}$

$= 1-\left ( \frac{5}{9} -\frac{6}{9} \right )^{2} :\frac{4}{27}$

$= 1- \left ( \frac{-1}{9} \right )^{2}.\frac{27}{4}$

$= 1 - \frac{1}{81}.\frac{27}{4}$

$= 1 - \frac{1}{12} = \frac{11}{12}$

c. $\left [ 1 -\left ( \frac{3}{8} - \frac{5}{12} \right ).6 + \frac{1}{3} \right ].4$

$= \left [ \left ( \frac{9}{24} -\frac{10}{24} \right ).6+\frac{1}{3} \right ].4$

$= \left [ \frac{-1}{24}.6 +\frac{1}{3} \right ].4$

$= \left [ \frac{-1}{4} + \frac{1}{3} \right ].4$

$= \frac{1}{12}.4 =\frac{1}{3}$

d. $0,8 : \left \{ 0,2 - 7. \left [ \frac{1}{6}+\left ( \frac{5}{21}-\frac{5}{14} \right ) \right ] \right \}$

$= \frac{4}{5}:\left \{ 0,2 - 7.\left [ \frac{1}{6} + \left ( \frac{5}{21} - \frac{5}{14} \right ) \right ] \right \}$

$= \frac{4}{5}:\left \{ \frac{1}{5} - 7 \right \}.\left [ \frac{7}{42} +\frac{-5}{42}\right ]$

$= \frac{4}{5}:\left \{ \frac{1}{5} - 7.\frac{1}{21} \right \}$

$= \frac{4}{5}:\left \{ \frac{1}{5} -\frac{1}{3} \right \}$

$= \frac{4}{5}:\frac{-2}{15} =\frac{4}{5}.\frac{-15}{2} = -6$