Đáp án:
Giải thích các bước giải:
A = $\frac{-7}{21}$ + (1 + $\frac{1}{3}$)
A = $\frac{-1}{3}$ + 1 + $\frac{1}{3}$
A = ($\frac{1}{3}$ + $\frac{-1}{3}$) + 1
A = 0 + 1
A = 1
B = $\frac{2}{15}$ + ($\frac{5}{9}$ + $\frac{-6}{9}$)
B = $\frac{2}{15}$ + $\frac{-1}{9}$ = $\frac{6}{45}$ + $\frac{-5}{45}$
B = $\frac{1}{45}$
C = $\frac{4}{20}$ + $\frac{16}{42}$ + $\frac{-3}{5}$ + $\frac{2}{21}$ + $\frac{-10}{21}$ + $\frac{3}{10}$
C = $\frac{1}{5}$ + $\frac{8}{21}$ + $\frac{-3}{5}$ + $\frac{2}{21}$ + $\frac{-10}{21}$ + $\frac{3}{10}$
C = ($\frac{1}{5}$ + $\frac{-3}{5}$) + ($\frac{8}{21}$ + $\frac{2}{21}$ + $\frac{-10}{21}$) + $\frac{3}{10}$
C = $\frac{-2}{5}$ + $\frac{3}{10}$ = $\frac{-4}{10}$ + $\frac{3}{10}$
C = $\frac{-1}{10}$
