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x+2x+3x+...+9x=90
x*9+(1+2+3+4+5+6+7+8+9)=90
x*9+45=90
x*9=90-45
x*9=45
x=45:9
x=5
~Hok Tốt~
K nhé MN????
\(x+2x+3x+...+9x=90\)
\(\Rightarrow\) \(x.\left(1+2+3+...+9\right)=90\)
\(\Rightarrow\) \(x.45=90\)
\(\Rightarrow\) \(x=2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) x+ 45 - [90+(-20)+5-(-45)]+3x
= x + 45 - [70+50]+3x
= x + 45 - 120 + 3 x
= ( x + 3x) + (45-120)
= 4x + (-75)
b) x+(294+13)+(94-13)+9x
= ( x + 9x ) + (294+13)+(94-13)
= 10x + 307+81
= 10x + 388
Trả lời:
a) x + 45 - [90 + (-20) + 5 - (-45)] + 3x
= (x + 3x) + 45 - (75 + 45)
= 4x + 45 - 75 - 45
= 4x + (45 - 45) - 75
= 4x + 0 - 75
= 4x - 75
b) x + (294 + 13) + (94 - 13) + 9x
= (9x + x) + 294 + 13 + 94 - 13
= 10x + (294 + 94) + (13 - 13)
= 10x + 388 + 0
= 10x + 388
Banh Bao Tong
![](https://rs.olm.vn/images/avt/0.png?1311)
a) x + 45 -[ 90 + (-20) + 5 - (-45)] +3x
= x +45 -( 90 - 20 + 5 + 45) + 3x
= x +45 -120 +3x
= -75 +4x
b) x +(-294 +13 -2x) +(94 -13) +9x
= x -281 -2x +81 +9x
= -200 +8x
![](https://rs.olm.vn/images/avt/0.png?1311)
X*(1+2+3+4+5+6+7+8+9+10)=-165
X*55=-165
X=-165/55=-3
111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
(1x + 9x) + (2x + 8x) + (3x + 7x) + (4x + 6x) + 5x + 10x = -165
10x^6 + 5x = -165
= 65x (-165)
= -100
![](https://rs.olm.vn/images/avt/0.png?1311)
x + 2x + 3x + ...+ 9x = 1800
x(1+2+3+...+9)=1800
45x=1800
x=1800:45
x=40
Vậy, x=40
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x+2x+3x+....+9x=990.\)
\(\Rightarrow x.\left(1+2+3+....+9\right)=990\)
\(\Rightarrow x.45=990\)
\(\Rightarrow x=990:45\)
\(\Rightarrow x=22\)
X duoc xuat hien so lan la:
1+2+3+4+5+6+7+8+9=45
x=990÷45=22
ĐS:22
-3x - 9x = - 30 - 90
- 12x = -120
x = -120 : -12
x = 10
90-3x=9x-30
90+30=9x+3x
120=12x
x=120/12
x=10