a) 17 + 23 = 40;   23 + 17 = 40

=> 17 + 23 = 23 + 17

b) (12 + 28) + 10 = 40 + 10 = 50

   12 + (28 + 10) = 12 + 38 = 50

=> (12 + 28) + 10 = 12 + (28 + 10)

c) 17.23 = 391;  23.17 = 391

=> 17.23 = 23.17

d) (5.6).3 = 30.3 = 90;  5.(6.3) = 5. 18 = 90

e) 23.(43+17) = 23. 60 = 1380

   23.43 + 23.17 = 989 + 391 = 1380

=> 23.(43+17) = 23.43 + 23.17

Thôi, để mk giải chi tiết cho, không lại bảo mk lười:

A=\(\dfrac{18}{26}+\dfrac{-5}{27}+\dfrac{-22}{86}+\dfrac{12}{39}+\dfrac{-32}{43}\)

A=\(\dfrac{9}{13}+\dfrac{-5}{27}+\dfrac{-11}{43}+\dfrac{4}{13}+\dfrac{-32}{43}\)

A=\(\left(\dfrac{9}{13}+\dfrac{4}{13}\right)+\left(\dfrac{-11}{43}+\dfrac{-32}{43}\right)+\dfrac{-5}{27}\)

A= 1+(-1)+\(\dfrac{-5}{27}\)

A=0+\(\dfrac{-5}{27}\)

A=\(\dfrac{-5}{27}\)

B=\(\dfrac{-10}{12}+\dfrac{8}{15}+\dfrac{-19}{56}+\dfrac{-3}{18}+\dfrac{28}{60}\)

B=\(\dfrac{-5}{6}+\dfrac{8}{15}+\dfrac{-19}{56}+\dfrac{-1}{6}+\dfrac{7}{15}\)

B=\(\left(\dfrac{-5}{6}+\dfrac{-1}{6}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)+\dfrac{-19}{56}\)

B= -1+1+\(\dfrac{-19}{56}\)

B=0+\(\dfrac{-19}{56}\)

B=\(\dfrac{-19}{56}\)

Ôi mỏi quá! Chúc bạn học tốt !

Help!

Cái nào rút gọn được thì rút gọn rồi quy đồng lên (hoặc sử dụng vài tính chất để tính nhanh nếu có thể)

A = \(\dfrac{18}{26}\) + (-\(\dfrac{5}{27}\)) + (-\(\dfrac{22}{86}\)) + \(\dfrac{12}{39}\) - \(\dfrac{32}{43}\)

A = \(\dfrac{9}{13}\) - \(\dfrac{5}{27}\) -  \(\dfrac{11}{43}\) + \(\dfrac{4}{13}\) - \(\dfrac{32}{43}\)

A = (\(\dfrac{9}{13}\) + \(\dfrac{4}{13}\)) - (\(\dfrac{11}{43}\) + \(\dfrac{32}{43}\)) - \(\dfrac{5}{27}\)

A = \(\dfrac{13}{13}\) - \(\dfrac{43}{43}\) - \(\dfrac{5}{27}\)

A = 1 - 1 - \(\dfrac{5}{27}\)

A = 0 - \(\dfrac{5}{27}\)

A = - \(\dfrac{5}{27}\)

B = -\(\dfrac{10}{12}\) + \(\dfrac{8}{15}\) - \(\dfrac{19}{56}\) + \(\dfrac{3}{-18}\) + \(\dfrac{28}{60}\)

B = - \(\dfrac{5}{6}\) + \(\dfrac{8}{15}\) - \(\dfrac{19}{56}\) - \(\dfrac{1}{6}\) + \(\dfrac{7}{15}\)

B = -(\(\dfrac{5}{6}\) + \(\dfrac{1}{6}\)) - \(\dfrac{19}{56}\) + (\(\dfrac{8}{15}\) + \(\dfrac{7}{15}\))

B = -1  - \(\dfrac{19}{56}\) + 1

B = - \(\dfrac{19}{56}\) 

a) x - 12= 91

   x= 91 + 12

    x= 103

b) 42 - x= 2 . 18

   42 - x= 36

           x = 42 - 36

              x = 6

c) (13 - x ) .28 =28

13 - x= 28 : 28 =1

x= 13 - 1

x= 12

a, x - 12 = 7 . 13

x - 12 = 91

x = 91 + 12

x = 103

b, 43 - x = 2.18

43 - x = 36

x = 43 - 36

x = 6

c, ( 13 - x ). 28 = 28

13 - x = 28 ÷ 28

13 -x = 1

x = 13 - 1

x = 12

a)  x - 12 = 14 x = 14 + 12 x = 26

b)  2 x - 13 = 3 . 17 2 x = 51 + 13 2 x = 64 x = 64 : 2 x = 32

c)  x - 43 = 2 . 18 x = 36 + 43 x = 79

d)  x - 14 . 39 = 0 x - 14 = 0 x = 14

e)  13 - x . 28 = 28 13 - x = 28 : 28 13 - x = 1 x = 13 - 1 x = 12

f) 22 . 35 - x = 22 35 - x = 1 x = 35 - 1 x = 34

g)  x - 24 : 2 = 18 x - 12 = 18 x = 39

h) 400 + 275 - x = 570 275 - x = 570 - 400 275 - x = 170 x = 275 - 170 x = 105

a) x – 12 = 14

x = 14 +12

x = 26

b) 2x – 13 = 3.17

2x = 51 + 13

2x = 64

x = 64 : 2

x = 32

c) x – 43 = 2.18

x = 36 +43

x = 79

d) (x – 14).39 = 0

x – 14 = 0

x = 14

e) (13 – x).28 = 28

13 – x = 1

13 – x = 1

x = 13 – 1

x = 12

f) 22.(35 – x) = 22

35 – x = 1

x = 35 – 1

x = 34

g) x – 24 : 2 = 18

x – 12 = 18

x = 39

h) 400 + (275 – x) = 570

275 – x = 570 – 400

275 – x = 170

x = 275 – 170

x = 105

a) 500

b) 2303                

c) 537                  

d) 35000

e) 90000

f) 380