(-69)x|-45|-31x|45|

=(-69)x45-31x45

=45x[(-69)-31]

=45x(-100)

=-4500

\(\left(-69\right)\times\left|-45\right|-31\times\left|45\right|\)

\(=\left(-69\right)\times45-31\times45\)

\(=45\left(-69-31\right)\)

\(=45\times100\)

\(=4500\)

1;

31.(45+69)+69.(45-31)

=31.45+69.31+69.45-69.31

=45.(69+31)+(69.31-69.31)

=45.100+0

=4500

2;

A=2x+3y+9x+8y

=>A=x.(2+9)+y.(8+3)

=>A=11x+11y

=>A=11.(x+y)mà x+y =10

=>A=11.10

=>A=110

Bài 1 .

31 . ( 45 + 69 ) + 69 . ( 45 - 31 )

= 31 . 45 + 69 . 31 + 69 . 45 - 69 . 31

= 45 . ( 69 + 31 ) + ( 69 . 31 - 69 . 31 )

= 45 . 100 + 0

= 4500

Bài 2 .

Ta có : A = 2x + 3y + 9x + 8y

\(\Rightarrow\) A = x . ( 2 + 9 ) + y . ( 3 + 8)

\(\Rightarrow\) A = 11x + 11y . Mà x + y = 10 nên :

\(\Rightarrow\) A = 11 . 10

\(\Rightarrow\) A = 110

Vậy A = 110

Tính nhanh

31 . ( 45 + 69 ) + 69 . ( 45 - 31 ) = 0

Tính nhanh :

a)8 x 45 + 55 x 8 

= 8x(45+55)

= 8x100

=800

28 x 69 + 31 x 28 

= 28x(69+31)

= 28x100

=2800

Ta có :

8 x 45 + 55 x 8 

= 8 x ( 45 + 55 )

= 8 x 100 

= 800

28 x 69 + 31 x 28 

= 28 x ( 69 + 31 )

= 28 x 100 

= 2800

mik tl trước mak 

-69.|-45|-31.|45|

-69.45-31.45

45.(-69-31)

45.-100

-4500

=-4500

-69 . |-45| - 31 . |45|.

= -69 . 45 - 31 . 45

= [ (-69) - 31 ] . 45

= (-100) . 45

= -4500.

#Học tốt.

Bài 6:

a)\(\left(-18\right)-\left(-3\right)-12\)

\(=\left(-18\right)+3-12\)

\(=-15-12\)

\(=-27\)

b)\(85.\left(35-27\right)-35.\left(85-27\right)\)

\(=85.35-85.27-35.85+35.27\)

\(=85.\left(35-27-35\right)+35.27\)

\(=85.\left(-27\right)+35.27\)

\(=27.\left(-85+35\right)\)

\(=27.\left(-50\right)\)

\(=-1350\)

c)\(\left(-45\right).69+31.\left(-45\right)\)

\(=\left(-45\right).\left(69+31\right)\)

\(=\left(-45\right).100\)

\(=-4500\)

Bài 7:

a)\(\left(2-x\right)+10=-14\)

\(\Rightarrow2-x=-24\)

\(\Rightarrow x=26\)

b)\(14.\left|x\right|=28\)

\(\Rightarrow\left|x\right|=2\)

\(\Rightarrow\orbr{\begin{cases}x=2\\x=-2\end{cases}}\)

c)\(31-\left(17+x\right)=55\)

\(\Rightarrow17+x=-24\)

\(\Rightarrow x=-41\)

(-18)-(-3)-12=-27

85.(35-27)-35.(85-27)=-1350

(-45).69+31.(-45)=-4500

(2-x)+10=-14

\(\Leftrightarrow\)(2-x)=-14-10

\(\Leftrightarrow\)2-x=-24

\(\Rightarrow\)x=2-(-24)

\(\Rightarrow\)x=26

14.lxl=28

\(\Leftrightarrow\)lxl=28:14

\(\Leftrightarrow\)lxl=2

\(\Rightarrow\)x=-2

a) \(-415+\left(-210\right)-367+62\)

= \(-625-367+62\)

= \(-992+62\)

= \(-930\)

b) \(-69\left|-45\right|-31\left|45\right|\)

= \(-69.45-31.45\)

= \(45\left(-69-31\right)\)

= \(45.\left(-100\right)\)

= \(-4500\)

c) \(3\left(-4\right)+2\left(-50\right)-12\)

= \(-12+\left(-100\right)-12\)

= \(-112-12\)

= \(-124\).

a)-415+(-210)-367+62

=[-415+(-210)]-(367-62)

=-625-305=-930

b)-69*|-45|-31*|45|

=-69*45-31*45

=(-69-31)*45

=-100*45

=-4500

c)3*(-4)+2*(-50)-12

=-12+100-12

=-24+100

=76

a) 45 x 76 + 90 x 12

= 45 x 76 + 45 x 2 x 12

= 45 x 76 + 45 x 24

= 45 x ( 76 + 24 ) 

= 45 x 100

= 4500

b) 2 x 31 x 12 + 4 x 6 x 69

= 24 x 31 + 24 x 69

= 24 x ( 31 + 69 )

= 24 x 100

= 2400

c) 36 x 28 + 36 x 82 + 64 x 69 + 64 x41

= 36 x ( 28 + 82 ) + 64 x ( 69 + 41 )

= 36 x 110 + 64 x 110

= 110 x ( 36 + 64 )

= 110 x 100

= 11 000

d) 156 ( x + 61)  = 82

=> x + 61 = \(\frac{82}{156}\)

=> x + 61 = \(\frac{41}{78}\)

=> x = \(\frac{41}{78}\)- 61

=> x = \(\frac{-4717}{78}\)

45 x 76 + 90 x 12 = 45 x 76 + 45 x 2 x 12

= 45 x 76 + 45 x 24

= 45 x (76 + 24)

= 45 x 100 

= 4500

b) 2 x 31 x 12 + 4 x  6 x 69 = 62 x 12 + 2 x 12 x 69

= 62 x 12 + 138 x 12

= (62 + 138) x 12

= 200 x 12 = 2400

a, 45 x 76 + 90 x 12

= ( 45 x 12 ) + ( 76 x 90 )

=  540     +   6840

=     7 380

c,

= 36 x ( 28 + 82 ) +  64 x ( 69 + 41 )

= 36 x  110    +   64 x 110

= 110 x ( 36 + 64 )

= 110 x 100

= 11000

Bài 6: Thực hiện phép tính

a)(-18)-(-3)-12

= (-18) + 3 - 12

= (-15) - 12

= - 3

b)85.(35-27)-35.(85-27)

= 85. 8 - 35. 58

= 680. 2030

= 1380400

c)(-45).69+31.(-45)

= (-45) . (69 + 31)

= (-45) . 100

= - 4500

Bài 7:Tìm x thuộc Z, biết:

a)(2-x)+10=-14

2-x = 14 - 10

2-x = 4

x = 2 - 4

x = - 2

b)14.|x|=28

|x| = 28 : 14

|x| = 2

⇒ x ϵ {2;-2}

a) ( 128,4 - 73,2 ) : 2,4 + 18,32 = 55,2 : 2,4 + 18,32 = 23 + 18,32 = 42,32

b) 210 : x = 14,92 - 6,52 

    210 : x = 8,4

             x = 210 : 8,4

             x = 25

c) mình không biết xin lỗi bạn nha 

k cho mình nha, yên tâm mình được việc lắm ( uy tín )