b: =402x2=804

130 x 2 + 130 x 8
= 130 x (2+8)
= 130 x 10
= 1300
402 x 9 – 402 x 7
= 402 x (9-7)
= 402 x 2
= 804

Áp dụng tính chất giao hoán, ta có:

68 130 x 9 = 9 x 68 130 = 613 170                                      

5 x 613 170 = 613 170 x 5 = 3 065 850

Áp dụng tính chất kết hợp, ta có:

9 x 68 130 x 5 = 613 170 x 5 = 3 065 850                           

5 x 9 x 68 130 = 5 x (9 x 68 130) = 5 x 613 170 = 3 065 850

(x + 1) + (x + 3) + (x + 5) + (x + 7) + (x + 9) = 130

=> x + 1 + x + 3 + x + 5 + x + 7 + x + 9 = 130

=> (x + x + x + x + x) + (1 + 3 + 5 + 7 + 9) = 130

=> 5x + \(\frac{\left(1+9\right)\cdot5}{2}\)= 130

=> 5x + 25 = 130

=> 5x = 105

=> x = 105 : 5 = 21

( x + 1 ) + ( x + 3 ) + ( x + 5 ) + ( x + 7 ) + ( x + 9 ) = 130 

x + 1 + x + 3 + x + 5 + x + 7 + x + 9 = 130 

5x + 25 = 130 

5x = 130 - 125 

5x = 105 

x = 21

(x+1)+(x+3)+(x+5)+(x+7)+(x+9)=130

(x+x+x+x+x)+(1+3+5+7+9)=130

5x+25=130

5x=130-25

5x=105

x=105:5

x=21

Hok tốt !!!!!!!!!!!!!!!!!!!!!

c: \(\Leftrightarrow x+16=2\cdot7=14\)

hay x=-2

1)

a)2x+26-84+7x=-130

(2x+7x)+(-84+26)=-130

9x-58=-130

9x=-130+58

9x=-72

x=-72/9

x=-8

Vậy x=-8

b)-6x+12+12-8x=-130

(-6x-8x)+(12+12)=-130

-14x+24=-130

-14x=-130-24

-14x=-154

x=-154/(-14)

x=11

Vậy x=11

c)4x-26-8=3x-69

4x-3x=-69+26+8

x=-35

Vậy x=-35

a: \(=\dfrac{3}{2}\cdot\dfrac{4}{3}\cdot...\cdot\dfrac{2001}{2000}=\dfrac{2001}{2}\)

b: \(=10.1\left(340+120-270\right)=10.1\cdot190=101\cdot19=1919\)

c: \(=24\%+8\%+59\%+9\%=1\)

a)  x = 64 : 8 = 8

b)  x = 60 : − 15 = − 4

c) 

12 x = 30 − 6 12 x = 24       x = 24 : 12       x = 2

d)

− 11 . x = 130 − 9 − 11 . x = 121                x = 121 : − 11                x = − 11