a)\(\dfrac{-3}{8}\)và\(\dfrac{5}{-12}\)

\(\dfrac{-3}{8}\)=\(\dfrac{-9}{24}\)      \(\dfrac{5}{-12}\)=\(\dfrac{-5}{12}\)=\(\dfrac{-10}{24}\)

Vì\(\dfrac{-9}{24}\)>\(\dfrac{-10}{24}\)nên\(\dfrac{-3}{8}\)>\(\dfrac{5}{-12}\)

b)\(\dfrac{3131}{5252}\)và\(\dfrac{31}{52}\)

\(\dfrac{31}{52}\)=\(\dfrac{3131}{5252}\)

Vì\(\dfrac{3131}{5252}\)=\(\dfrac{3131}{5252}\)nên \(\dfrac{3131}{5252}\)=\(\dfrac{31}{52}\)

\(\)

=\(=1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{109}-\dfrac{1}{101}\)

=\(1-\left(\dfrac{1}{3}-\dfrac{1}{3}\right)+\left(\dfrac{1}{5}-\dfrac{1}{5}\right)+\left(\dfrac{1}{7}-\dfrac{1}{7}\right)+...-\dfrac{1}{101}\)

=\(1-\dfrac{1}{101}=\dfrac{101}{101}-\dfrac{1}{101}=\dfrac{100}{101}\)

a)Các điểm thuộc đường thẳng BD là:B,C,D

Các điểm không thuộc đường thẳng BD là:A,E

b)Cặp đường thẳng song song:AB//DE

c)AB cắt AC tại A

AB cắt BD tại B

DE cắt BD tại D

DE cắt AE tại E

AE cắt BD tại C

2)đoạn thẳng AB là : OB-OA=6-4=2(cm)

Vì M là trung điểm của AB nên AM=AB.1/2=2:2=1(cm)

Ta có OM=OA+AM=4+1=5(cm)

Vậy OM dài 5 cm

$a)$ Ta có :

$\frac{2}{9}=\frac{6}{27}$

$\frac{1}{3}=\frac{9}{27}$

Vì $\frac{5}{27}<\frac{6}{27}<\frac{9}{27}$ nên $\frac{5}{27}<\frac{2}{9}<\frac{1}{3}$

$\Rightarrow$ Đội $2$ làm được khối lượng công việc nhiều nhất, đội $3$ làm được khối lượng công việc ít nhất.

$b)$ Nếu làm chung thì mỗi giờ cả ba đội làm được là :

$\frac{2}{9}+\frac{1}{3}+\frac{5}{27}=\frac{20}{27}$ (công việc )

a)x-\(\dfrac{2}{3}\)=\(\dfrac{-5}{12}\)

x=\(\dfrac{-5}{12}\)+\(\dfrac{2}{3}\)

x=\(\dfrac{-5}{12}\)+\(\dfrac{8}{12}\)

x=\(\dfrac{3}{12}\)=\(\dfrac{1}{4}\)

b)\(\dfrac{8}{5}\):x=\(\dfrac{-2}{3}\)

x=\(\dfrac{8}{5}\):\(\dfrac{-2}{3}\)

x=\(\dfrac{8}{5}\).\(\dfrac{-3}{2}\)

x=\(\dfrac{-12}{5}\)

c)1-\(\dfrac{3}{7}\).X=-\(\dfrac{2}{7}\)

\(\dfrac{3}{7}\).x=1-(-\(\dfrac{2}{7}\))

\(\dfrac{3}{7}\).x=1+\(\dfrac{2}{7}\)

\(\dfrac{3}{7}\).x=\(\dfrac{7}{7}\)+\(\dfrac{2}{7}\)

\(\dfrac{3}{7}\).x=\(\dfrac{9}{7}\)

x=\(\dfrac{9}{7}:\dfrac{3}{7}=\dfrac{9}{7}.\dfrac{7}{3}=3\)

a)\(\dfrac{-2}{7}\)+\(\dfrac{2}{7}\):\(\dfrac{3}{5}\)

=\(\dfrac{-2}{7}\)+\(\dfrac{2}{7}\).\(\dfrac{3}{5}\)

=\(\dfrac{-2}{7}\)+\(\dfrac{6}{35}\)

=\(\dfrac{-10}{35}\)+\(\dfrac{6}{35}\)

=\(\dfrac{-4}{35}\)

b)\(\dfrac{-8}{19}\)+\(\dfrac{-4}{21}\)-\(\dfrac{17}{21}\)+\(\dfrac{27}{19}\)

=(\(\dfrac{-8}{19}\)+\(\dfrac{27}{19}\))-(\(\dfrac{17}{21}\)+\(\dfrac{-4}{21}\))

=\(\dfrac{19}{19}\)-\(\dfrac{13}{21}\)

=1-\(\dfrac{13}{21}\)

=\(\dfrac{21}{21}\)-\(\dfrac{13}{21}\)

=\(\dfrac{8}{21}\)

c)\(\dfrac{6}{5}\).\(\dfrac{3}{13}\)-\(\dfrac{6}{5}\).\(\dfrac{16}{13}\)

=\(\dfrac{6}{5}\).(\(\dfrac{3}{13}\)-\(\dfrac{16}{13}\))

=\(\dfrac{6}{5}\).\(\dfrac{-13}{13}\)

=\(\dfrac{6}{5}\).\(-1\)

=\(\dfrac{-6}{5}\)