BM
1
K
Khách
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30 tháng 11 2018
x khác 1
\(N=\frac{\left(x+2\right)\left(x-1\right)}{\left(x-1\right)\left(x^2+x+1\right)}-\frac{2\left(x^2+x+1\right)}{\left(x-1\right)\left(x^2+x+1\right)}+\frac{2x^2+4}{\left(x+1\right)\left(x^2+x+1\right)}\)
\(N=\frac{x^2+2x-x-2-2x^2-2x-2+2x^2+4}{\left(x-1\right)\left(x^2+x+1\right)}=\frac{x^2-x}{\left(x-1\right)\left(x^2+x+1\right)}=\frac{x\left(x-1\right)}{\left(x-1\right)\left(x^2+x+1\right)}\)
\(=\frac{x}{x^2+x+1}\)
Xét hiệu 1/3-N=\(\frac{1}{3}-\frac{x}{x^2+x+1}=\frac{x^2+x+1-3x}{3\left(x^2+x+1\right)}=\frac{x^2-2x+1}{3\left(x^2+x+1\right)}=\frac{\left(x-1\right)^2}{3\left(x^2+x+1\right)}>0\)với mọi x khác 1
=> 1/3 >N
DX
23 tháng 12 2022
\(Q=\left(\dfrac{x+1}{\left(x-1\right)^2}+\dfrac{1}{x-1}\right).\dfrac{x-1}{x}-\dfrac{2}{x-1}=\left(\dfrac{2}{x-1}\right)-\left(\dfrac{2}{x-1}\right)=0\)
28 tháng 6 2017
a.ĐKXĐ \(x\ne0,x\ne1\),\(x\ne-1\)
B=\(\frac{4}{\left(x-1\right)^2}-\frac{x^2-1}{x^3-x}.\frac{x^3+x}{\left(x-1\right)^2}\)=\(\frac{4}{\left(x-1\right)^2}-\frac{x.\left(x^2+1\right)\left(x^2-1\right)}{x\left(x^2-1\right)\left(x-1\right)^2}\)=\(\frac{4}{\left(x-1\right)^2}-\frac{x^2+1}{\left(x-1\right)^2}\)
=\(\frac{3-x^2}{\left(x-1\right)^2}\)
b.TH1 x=3\(\Rightarrow\)B=\(\frac{3-3^2}{2^2}=\frac{-3}{2}\)
TH2 x=-1\(\Rightarrow\)B=\(\frac{3-\left(-1\right)^2}{4}=\frac{1}{2}\)
c.B=-1\(\Leftrightarrow\frac{3-x^2}{\left(x-1\right)^2}=-1\)\(\Leftrightarrow x^2-3=x^2-2x+1\)\(\Leftrightarrow2x=4\Leftrightarrow x=2\)
d.B+2=\(\frac{3-x^2}{\left(x-1\right)^2}+2=\frac{x^2-4x+5}{\left(x-1\right)^2}=\frac{\left(x-2\right)^2+1}{\left(x-1\right)^2}\ge0\)với mọi x\(\Rightarrow B\)>-2
LH
1
30 tháng 1 2022
a: \(P=\dfrac{4x-6-x+1}{2x-3}:\left(\dfrac{6x+1}{2x^2-3x+2x-3}+\dfrac{x}{x+1}\right)\)
\(=\dfrac{3x-5}{2x-3}:\left(\dfrac{6x+1}{\left(x+1\right)\left(2x-3\right)}+\dfrac{x}{x+1}\right)\)
\(=\dfrac{3x-5}{2x-3}:\dfrac{6x+1+2x^2-3x}{\left(x+1\right)\left(2x-3\right)}\)
\(=\dfrac{3x-5}{\left(2x-3\right)}\cdot\dfrac{\left(2x-3\right)\left(x+1\right)}{2x^2+3x+1}\)
\(=\dfrac{3x-5}{2x+1}\)
b: \(P-\dfrac{3}{2}=\dfrac{3x-5}{2x+1}-\dfrac{3}{2}=\dfrac{6x-10-6x-3}{2\left(2x+1\right)}=\dfrac{-7}{2\left(2x+1\right)}\)
a) \(Q=\frac{x^4-x^2+2x+2}{x^4+x^3+x+1}\)
\(Q=\frac{x^2\left(x^2-1\right)+2\left(x+1\right)}{x^3\left(x+1\right)+\left(x+1\right)}\)
\(Q=\frac{x^2\left(x+1\right)\left(x-1\right)+2\left(x+1\right)}{\left(x+1\right)\left(x^3+1\right)}\)
\(Q=\frac{\left(x+1\right)\left[x^2\left(x-1\right)+2\right]}{\left(x+1\right)\left(x^3+1\right)}\)
\(Q=\frac{x^3-x^2+2}{x^3+1}\)
b) \(Q=\left|Q\right|=\frac{x^3-x^2+2}{x^3+1}\)