Question

Answer 1

=>21x+210=20

=>21x=-190

hay x=-190/21

Answer 2

\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+20\right)=20\)

\(\Rightarrow21x+\left(1+2+...+20\right)=20\)

\(\Rightarrow21x+\left[\left(20+1\right).20:2\right]=20\)

\(\Rightarrow21x+210=20\)

\(\Rightarrow21x=-190\Rightarrow x=-\dfrac{190}{21}\)

Answer 3

\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+20\right)=20\\ =>\left(x+x+x+...+x\right)+\left(1+2+...+20\right)=20\\ =>21x+\dfrac{\left(20+1\right).20}{2}=20\\ =>21x+21.10=20\\ =>21x=-190\\ =>x=-\dfrac{190}{21}\)

\(Mà : x\in Z\)

\(=>x\in\varnothing\)

 

Answer 4

`x + (x + 1) + (x + 2) + ... + (x + 20)  =20`

số số hạng là : `(20 - 1) : 1 + 1 =20( số số hạng )`

tổng là `: (20 + 1) xx 20  : 2 = 210`

`x + (x + 1) + (x + 2) + ... + (x + 20) = 20`

`=> x + x +1 + x+2+...+x+20=20`

`=>(x+x+x+..+x )+(1 + 2 + ... + 20) = 20`

`=> 21x + 210 = 20`

`=>  21x           = 20 - 210`

`=> 21x             = -190`

`=>    x               = -190 : 21`

`=>    x               = -190/21`

Answer 5

\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+20\right)=20\)

\(\Leftrightarrow x+x+1+x+2+...+x+20=20\)

\(\Leftrightarrow21x+210=20\)

\(\Leftrightarrow21x=-190\)

\(\Leftrightarrow x=-\dfrac{190}{21}\)