Giải bài 4 trang 16 toán 7 tập 1 chân trời sáng tạo

a) $\frac{3}{7}$ . $\left( -\frac{1}{9} \right)$ + $\frac{3}{7}$ . $\left( -\frac{2}{3} \right)$

= $\frac{3}{7}$ . $\left[ \left( -\frac{1}{9} \right) \right.$ + $\left. \left( -\frac{2}{3} \right) \right]$

= $\frac{3}{7}$ . $\left[ \left( -\frac{1}{9} \right) \right.$ + $\left. \left( -\frac{6}{9} \right) \right]$

= $\frac{3}{7}$ . $\left( -\frac{7}{9} \right)$ = $-\frac{1}{3}$

b) $\left( \frac{-7}{13} \right)$ . $\frac{5}{12}$ + $\left( \frac{-7}{13} \right)$ . $\frac{7}{12}$ + $\frac{-7}{13}$ + $\left( \frac{-6}{13} \right)$

= $\left( \frac{-7}{13} \right)$ .  $\left( \frac{5}{12}+\frac{7}{12} \right)$  - $\frac{6}{13}$

= $\left( \frac{-7}{13} \right).1-\frac{6}{13}$ = -1 

c) $\left[ \left( \frac{-2}{3} \right) \right.$ + $\left. \frac{3}{7} \right]$: $\frac{5}{9}$+ $\left( \frac{4}{7}-\frac{1}{3} \right)$ :  $\frac{5}{9}$

=  $\left[ \left( \frac{-2}{3} \right) \right.$ + $\frac{3}{7}$ + $\left. \left( \frac{4}{7}-\frac{1}{3} \right) \right]$: $\frac{5}{9}$

= (-1 + 1) . $\frac{9}{5}$ = 0

d) $\frac{5}{9}$ : $\left( \frac{1}{11}-\frac{5}{22} \right)$ + $\frac{5}{9}$ : $\left( \frac{1}{15}-\frac{2}{3} \right)$

= $\frac{5}{9}:\left( \frac{-3}{22} \right)+\frac{5}{9}:\left( -\frac{3}{5} \right)$

= $\frac{5}{9}.\left( \frac{-22}{3} \right)+\frac{5}{9}.\left( -\frac{5}{3} \right)$

=$\frac{5}{9}.\left( \frac{-22}{3}-\frac{5}{3} \right)$

= $\frac{5}{9}.\left( \frac{-22}{3}-\frac{5}{3} \right)=\frac{5}{9}.(-9)=-5$

e) $\frac{3}{5}$ +  $\frac{3}{11}$ - $\left( -\frac{3}{7} \right)$  + $\left( -\frac{2}{97} \right)$ - $\frac{1}{35}$  - $\frac{3}{4}$

= $\left[ \frac{3}{5} \right.$ - $\left( -\frac{3}{7} \right)$ - $\left. \frac{1}{35} \right]$ +  [$\left[ \frac{3}{11} \right.$ - $\frac{3}{4}$  + $\left. \left( -\frac{23}{44} \right) \right]$+ $\left( -\frac{2}{97} \right)$   

= 1 + (-1) + $\left( -\frac{2}{97} \right)$ = $-\frac{2}{97}$