`(x - 2)/3 = (x + 1)/4`

`(x - 2) . 4 = (x + 1) . 3`

`<=> 4x - 8 = 3x + 3`

`<=> 4x - 3x = 3 + 8`

`<=> (4 - 3)x = 11`

`=> x = 11`

`=>` `x = 11`

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100x+(1+100).100/2=5750

100x+5050=5750

100x=700

x=7

X=7                  

\(\left(x+1\right)+\left(x+2\right)+...+\left(x+9\right)=90\)

Ta có 9 SSH (từ 1 đến 9)

9.x+(1+2+3+...+9)=90

9x+(9+1).9:2=90

9x+45=90

9x=90-45=45

x=45:9

x=5

(x+1)+(x+2)+...+(x+9)=90

Ta có 9 SSH (từ 1 đến 9)

9.x+(1+2+3+...+9)=90

9x+(9+1).9:2=90

9x+45=90

9x=90-45=45

x=45:9

x=5

\(\left(x+1\right)+\left(x+2\right)+\left(x+3\right)+...+\left(x+9\right)=90\)

\(\Rightarrow\left(x+x+x+...+x\right)+\left(1+2+3+...+9\right)=90\)

\(\Rightarrow9x+45=90\)

\(\Rightarrow9x=90-45\)

\(\Rightarrow9x=45\Rightarrow x=5\)

\(\left(x-1\right)^2+\left(y+3\right)^2=0\left(1\right)\)

Ta thấy \(\left\{{}\begin{matrix}\left(x-1\right)^2\ge0,\forall x\\\left(y+3\right)^2\ge0,\forall y\end{matrix}\right.\)

\(\left(1\right)\Leftrightarrow\left\{{}\begin{matrix}\left(x-1\right)^2=0\\\left(y+3\right)^2=0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x-1=0\\y+3=0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=-3\end{matrix}\right.\)

=> \(\left[{}\begin{matrix}\left(x-1\right)^2=0\\\left(y+3\right)^2=0\end{matrix}\right.\)

=> \(\left[{}\begin{matrix}\left(x+1\right)^2=0^2\\\left(y+3\right)^2=0^2\end{matrix}\right.\)

=> \(\left[{}\begin{matrix}x+1=0\\y+3=0\end{matrix}\right.\)

=> \(\left[{}\begin{matrix}x=-1\\y=-3\end{matrix}\right.\)

côn thức[ số đầu + số cuối ] . các số hạng / 2 = kết quả

[1+x].b/2=55

=55.2=110

=[1+10].10/2=55

=x=10

tớ chỉ có thể giải thích thế này thôi nên thứ lỗi

a) \(4^x+4^{x+1}=80\)

\(\Rightarrow4^x+4^x.4=80\)

\(\Rightarrow4^x.\left(1+4\right)=80\)

\(\Rightarrow4^x.5=80\)

\(\Rightarrow4^x=16\)

\(\Rightarrow4^x=4^2\)

\(\Rightarrow x=2\)

Vậy x = 2