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\(\frac{-3}{14}\) - \(\frac{5}{-14}\)

= \(\frac{-3}{14}+\frac{5}{14}\)

= \(\frac{2}{14}\)

= \(\frac17\)

- \(\frac54\) - \(\frac34\)

= -(\(\frac54+\frac34\))

= - \(\frac84\)

= - 2

\(\frac{15}{6}-\frac{-10}{20}\)

= \(\frac52\) + \(\frac12\)

= \(\frac62\)

= 3

\(\frac{26}{-35}\) - \(\frac{6}{35}\)

= - (\(\frac{26}{35}\) + \(\frac{6}{35}\))

=- \(\frac{32}{35}\)

a, \(\frac{2}{5}.\frac{1}{3}-\frac{2}{15}:\frac{1}{5}+\frac{3}{5}.\frac{1}{3}\)

\(=\frac{1}{3}.\left(\frac{2}{5}+\frac{3}{5}\right)-\frac{2}{15}.5\)

\(=\frac{1}{3}.1-\frac{2}{3}\)

\(=\frac{1}{3}-\frac{2}{3}\)

\(=\frac{-1}{3}\)

b, \(\left(6-2\frac{4}{5}\right).3\frac{1}{8}+1\frac{3}{8}:\frac{1}{4}\)

\(=\left(6-\frac{14}{5}\right).\frac{25}{8}+\frac{11}{8}.4\)

\(=\frac{16}{5}.\frac{25}{8}+\frac{11}{2}\)

\(=10+\frac{11}{2}\)

\(=\frac{31}{2}\)

1/3×(3/5+2/5)-2/15×1/5

1/3×1-2/15×1/5

1/3-2/15×1/5

1/3-2/75

25/75-2/75

23/75

(6-14/5)×25/8-11/8:4/1

16/5×25/8-11/8:4/1

10/1-11/8:4/1

10/1-11/8×1/4

10/1-11/32

320/32-11/32

309/32

=\(\left(4-2+3\right)\cdot\frac{-1}{2}\)

=\(5\cdot\left(\frac{-1}{2}\right)\)

=\(\frac{5\cdot\left(-1\right)}{2}\)

=\(\frac{-6}{2}\)

\(=\left(-3\right)\)

Có 2 trg hợp nhé: Nếu x là dấu nhân thì thực hiện theo phép nhân

Nếu x là ẩn số thì ko làm đc nhé vì ko có kết quả 

Nên làm theo trường hợp 1

\(4.\frac{-1}{2}-2.\frac{-1}{2}+3.\frac{-1}{2}\)\(=\)\(\left(\frac{-1}{2}\right).\left(4-2+3\right)=\left(\frac{-1}{2}\right).5=\frac{-1.5}{2}=\frac{-5}{2}\)

Câu a:

- \(\frac{15}{8}\) + \(\frac78-4\)

= - \(\frac88\) - 4

= - 1 - 4

= - 5

Câu b:

- \(\frac57\).\(\frac{2}{11}\) \(-\frac57\).\(\frac{9}{11}\) + \(\frac67\)

= - \(\frac57\).(\(\frac{2}{11}\) + \(\frac{9}{11}\)) + \(\frac67\)

= - \(\frac57\). 1 + \(\frac67\)

= - \(\frac57\) + \(\frac67\)

= - \(\frac17\)

1/ Bg

\(\frac{21^4}{27.\left(-343\right)}\)= \(\frac{\left(3.7\right)^4}{3^3.\left(-7\right)^3}\)

= \(\frac{3^4.7^4}{3^3.\left(-7\right)^3}\)

= \(\frac{3.\left(-7\right)}{1.1}\)

= 3.(-7)

= -21

2/ Bg

Ta có: \(\frac{a}{4}=\frac{b}{5}=\frac{c}{2}\)và a + b - c = 21                      (a, b, c thuộc Z)

Áp dụng tính chất dãy tỉ số bằng nhau, ta có:

\(\frac{a}{4}=\frac{b}{5}=\frac{c}{2}=\frac{a+b-c}{4+5-2}=\frac{21}{7}\)= 3

=> a = 3.4 = 12

=> b = 3.5 = 15

=> c = 3.2 = 6

Vậy a = 12, b = 15 và c = 6

a,    6/7+5/9+8/7-2/9=(6/7+8/7)+(5/9-2/9)=14/7+3/9=2+1/3=7/3

b, 5+7/3=22/3

a/ \(\frac{6}{7}+\frac{5}{9}+\frac{8}{7}-\frac{2}{9}\)

= \(\left(\frac{6}{7}+\frac{8}{7}\right)+\left(\frac{5}{9}-\frac{2}{9}\right)\)

=  \(2+\frac{1}{3}\)

= \(\frac{7}{3}\)

b/ 5+\(2\frac{1}{3}\)

= 5 + \(\frac{7}{3}\)

= \(\frac{22}{3}\)

Câu 1 :

A= 1.2.3...9-1.2.3...8-1.2.3...8²

  = 1.2.3...8. ( 9 - 1 - 8 )

  = 1.2.3...8.0

  = 0

b)=(2/3 +2/7 - 2/28)/(-3/3 -3/7 + 3/28)

=[2(1/3+1/7-1/28)]/[(-3)(1/3+1/7-1/28)]

=2/-3 

=-2/3

\(=\frac{-\frac{1}{4}.-\frac{1}{5}}{\frac{5}{9}-\frac{13}{12}}\)

\(=\frac{\frac{1}{20}}{\frac{1}{4}}\)

\(=\frac{1}{20}:\frac{1}{4}\)

\(=\frac{1}{5}\)