bài 23 : a) =8 -125: 25 +12x4                                                                                     = 8- 5+12x4                                                                                               = 8-5+48                                                                                                   = 3+48                                                                                                       = 51

a) 70-5(x-3)=45

<=>70-5x+15=45

<=>-5x=-40

<=>x=8

c)130-(100+x)=25

<=>130-100-x=25

<=>x=5

e)5(x+12)+22=92

<=>5x+60+22=92

<=>5x=10

<=>x=2

Bài 14: 

a; (- 6).9 = -54

b; (-12).(-987) = 11844

c; 90.(-108).(-3)

= -9720.(-3)

= 29160

Bài 14 

d; 29.(-78).(-9).(-11)

= -2262.(-9).(-11)

= 20358.(-11)

= - 223938

e; 6.(-4)².(-10)² +5²

= 6.16.100 + 25

= 96.100 + 25

= 9600 + 25

= 9625;

f; (-7).(-7).(-7) + 7³

= -7³ + 7³

= 0

a; -156 - (-26) = - 156 + 26 = -130;

b; (-156) - 76 = - (156 + 76) = - 232

c;  -156 - [(-28) - (-143)] = -156 - [ -28 + 143] = -156 - 115 = - 271

\(a.\) \(\left(-156\right)-\left(-26\right)=\left(-156\right)+26=130\)

\(b.\) \(\left(-156\right)-76=-\left(156+76\right)=-232\)

\(c.\) \(\left(-156\right)-\left(-28\right)-\left(-143\right)\)

\(=\left(-156\right)+28+143\)

\(=\left(-128\right)+143\)

\(=\left(143-128\right)=15\)

(Chia hết cho 2)
+) Ta có: A = 2 + 2^2 + 2^3 + ... + 2^12
⇒ A = 2 (1 + 2 + 2^2 + ... + 2^11)
Vậy A chia hết cho 2

(Chia hết cho 3)
+) Ta có: A = 2 + 2^2 + 2^3 + ... + 2^12
⇒ A = (2 + 2^2) + (2^3 + 2^4) ... (2^11 + 2^12)
⇒ A = 2(1 + 2) + 2^3(1 + 2) + ... + 2^11(1 + 2)
⇒ A = 2.3 + 2^3.3 + 2^11.3
⇒ A = 3(2 + 2^3 + ... + 2^11)
Vậy A chia hết cho 3

(Chia hết cho 6)
+) Vì A chia hết cho 2; A chia hết cho 3
⇒ A chia hết cho 6

(Chia hết cho 7 mình ko biết làm <3)

a; -\(\dfrac{3}{26}\).(-\(\dfrac{15}{19}\)) + \(\dfrac{2}{9}\) .(- \(\dfrac{3}{26}\))

=   - \(\dfrac{3}{26}\).( - \(\dfrac{15}{19}\) + \(\dfrac{2}{9}\))

= - \(\dfrac{3}{26}\).(-\(\dfrac{97}{171}\))

=  \(\dfrac{97}{1482}\)

b; (-\(\dfrac{2}{5}\)).\(\dfrac{4}{15}\) + (-\(\dfrac{3}{10}\)).\(\dfrac{4}{15}\)

= \(\dfrac{4}{15}\).(-\(\dfrac{2}{5}\) - \(\dfrac{3}{10}\))

= \(\dfrac{4}{15}\).(-\(\dfrac{7}{10}\))

= - \(\dfrac{14}{75}\)

Đăng bài lên nhé.

Câu hỏi bạn ơi 

\(\dfrac{-777}{546}=\dfrac{\left(-777\right):21}{546:21}=\dfrac{-37}{26}\)

Câu 10 phần ở trên là phần a còn ở dưới là phần b nha mn

\(\dfrac{17}{5}.\left(-\dfrac{31}{125}\right).\dfrac{1}{2}.\dfrac{10}{17}.\left(-\dfrac{1}{8}\right)\\=\dfrac{17}{5}.\dfrac{10}{17}.\left(-\dfrac{31}{125}\right).\left(-\dfrac{1}{8}\right)\\ =2.\dfrac{31}{1000}\\ =\dfrac{31}{500} \)

a,\(\left[\dfrac{11}{4}.\left(-\dfrac{5}{9}\right)-\dfrac{4}{9}.\dfrac{11}{4}\right].\dfrac{8}{33}\\ =\left[\dfrac{11}{4}.\left(-1\right)\right].\dfrac{8}{33}\\ =-\dfrac{11}{4}.\dfrac{8}{33}\\ =-\dfrac{2}{3}.\)

b, \(-\dfrac{3}{5}+\dfrac{8}{5}.\left(\dfrac{43}{56}+\dfrac{5}{24}-\dfrac{21}{63}\right)\\ =-\dfrac{3}{5}+\dfrac{8}{5}.\dfrac{9}{14}\\ =-\dfrac{3}{5}+\dfrac{36}{35}\\ =\dfrac{3}{7}.\)

\(\dfrac{1}{7}.\dfrac{5}{9}+\dfrac{5}{9}.\dfrac{1}{7}.\dfrac{5}{9}+\dfrac{3}{7}\)

\(=\dfrac{5}{9}.\left(\dfrac{1}{7}+\dfrac{1}{7}+\dfrac{3}{7}\right)\)

\(=\dfrac{5}{9}.\dfrac{5}{7}=\dfrac{25}{63}\)

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