\(2015-\left|x-2015\right|=x\)

\(\Leftrightarrow\left|x-2015\right|=2015-x\)

\(\Leftrightarrow\orbr{\begin{cases}x-2015=2015-x\\x-2015=-\left(2015-x\right)\end{cases}}\)

\( TH1:x-2015=2015-x\)

\(\Leftrightarrow2x=4030\)

\(\Leftrightarrow x=\frac{4030}{2}\)

\(\Leftrightarrow x=2015\)

\(TH2:x-2015=-\left(2015-x\right)\)

\(\Leftrightarrow x-2015=x-2015\)

Vậy x = 2015

2015-|x-2015|=x

|x-2015|=2015-x

x-2015=2015-x

hoặc x-2015=x-2015

x=2015

0=0

Vậy x=2015

k cho mình nha

\(A=\frac{1}{1.2}+\frac{1}{2.3}+....+\frac{1}{99.100}\)

\(\Rightarrow A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-......-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\)

\(\Rightarrow A=1-\frac{1}{100}\)

\(\Rightarrow A=\frac{99}{100}\)

Vậy \(A=\frac{99}{100}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)

\(A=1-\frac{1}{100}\)

\(A=\frac{99}{100}\)

Ta có: \(M=x+y-z-2x+y+z-2+x+y\)

    \(\Rightarrow M=\left(x-2x+x\right)+\left(y+y+y\right)-\left(z-z\right)\)

    \(\Rightarrow M=3y\) 

          \(N=x-x+y-z+x\)

    \(\Rightarrow N=x+y-z\)

Ta lại có: \(M+N=3y+x+y-z\)

         \(\Rightarrow M+N=x+4y-z\)

  Vậy tổng \(M+N=x+4y-z\)

Ta có: M=[x+(y-z)-2x]+y+z-(2-x-y)=x+y-z-2x+y+z-2+x+y=3x

N=x-[x-(y-z)-x]=x-[x-y+z-x]=x-x+y-z+x=x+y-z

ta lại có:

M+N=3x+x+y-z=4x+y-z

M-N=3x-(x+y-z)=3x-x-y+z=2x-y+z

3. Tìm x biết: |15-|4.x||=2019

\(\Rightarrow\orbr{\begin{cases}15-\left|4x\right|=2019\\15-\left|4x\right|=-2019\end{cases}\Rightarrow\orbr{\begin{cases}\left|4x\right|=-2004\\\left|4x\right|=2034\end{cases}}}\)

vì \(4x\ge0\)\(\Rightarrow\)|4x|=2043\(\Rightarrow4x=2034\Rightarrow x=508,5\)

KL: x=508,5

SGK toán 7

2015 nhé

=> |x-2015|=2015-x

=>x-2015<0

=>x<-2015