Bài 1: Tính a, 1/2 – (1/3 + 1/10) b, 1/12 – (-1/6 – 1/4) c, 1/2 – (-1/3) + 1/23 + 1/6 d, 2/5 + (-4/5) + (-1/2) Bài 2: a, tìm ba cách viết số hữu tỉ -1

Đáp án:

Giải thích các bước giải:

1) 

a) $\frac{1}{2}-(\frac{1}{3}+\frac{1}{10})\\=\frac{1}{2}-\frac{13}{30}\\=\frac{1}{15}$\

b) $\frac{1}{12}-(-\frac{1}{6}-\frac{1}{4})\\=\frac{1}{12}+\frac{5}{12}\\=\frac{1}{2}$

c) $\frac{1}{2}-(-\frac{1}{3})+\frac{1}{23}+\frac{1}{6}\\=\frac{5}{6}+\frac{1}{23}+\frac{1}{6}\\=\frac{121}{138}+\frac{1}{6}\\=\frac{24}{23}$

d) $\frac{2}{5}+(-\frac{4}{5})+(-\frac{1}{2})\\=-\frac{2}{5}-\frac{1}{2}\\=-\frac{9}{10}$

Bài 2:

$-\frac{1}{5}-\frac{6}{25}; -\frac{1}{10}-\frac{17}{50}; -\frac{1}{20}-\frac{39}{100}$

b) Không có bởi vì dương cộng dương bằng dương

Bài 3:

a) $x+\frac{1}{3}=\frac{2}{5}-(-\frac{1}{3})\\\Leftrightarrow x+\frac{1}{3}=\frac{2}{5}+\frac{1}{3}\\\Leftrightarrow x=\frac{2}{5}$

b) $\frac{7}{4}-(x+\frac{5}{3})=-\frac{12}{5}\\\Leftrightarrow -x+\frac{1}{12}=-\frac{12}{5}\\\Leftrightarrow x=\frac{149}{60}$

c) $x-(\frac{17}{2}-(-\frac{3}{7}+\frac{5}{3}))=-\frac{1}{3}\\\Leftrightarrow x-(\frac{17}{2}-\frac{26}{21})=-\frac{1}{3}\\\Leftrightarrow x-\frac{305}{42}=-\frac{1}{3}\\\Leftrightarrow x=\frac{319}{42}$

d) $\frac{9}{2}-(\frac{2}{3}-(x+\frac{7}{4}))=-\frac{5}{4}\\\Leftrightarrow \frac{23}{6}+(x+\frac{7}{4})=-\frac{5}{4}\\\Leftrightarrow x+\frac{7}{4}=-\frac{61}{12}\\\Leftrightarrow x=-\frac{41}{6}$