`a,m=1`

`=>(2x+1)/x=(2x)/(x-1)`

`<=>2x^2-x-1=2x^2`

`<=>-x-1=0`

`<=>x=-1`

`b,(2x+m)/x=(2x)/(x-1)`

`<=>2x^2=2x^2-2x+mx-m`

`<=>mx-2x=m`

`<=>x(m-2)=m`

PT có nghiệm duy nhất

`<=>m-2 ne 0<=>m ne 2`

PT vô nghiệm

`<=>m-2=0,m ne 0`

`<=>m=2`

PT có vô số nghiệm

`<=>m=2,m=2` vô lý.

a: Thay m=-5 vào (1), ta được:

\(x^2+2\left(-5+1\right)x-5-4=0\)

\(\Leftrightarrow x^2-8x-9=0\)

=>(x-9)(x+1)=0

=>x=9 hoặc x=-1

b: \(\text{Δ}=\left(2m+2\right)^2-4\left(m-4\right)=4m^2+8m+4-4m+16=4m^2+4m+20>0\)

Do đó: Phương trình luôn có hai nghiệm phân biệt 

\(\dfrac{x_1}{x_2}+\dfrac{x_2}{x_1}=-3\)

\(\Leftrightarrow x_1^2+x_2^2=-3x_1x_2\)

\(\Leftrightarrow\left(x_1+x_2\right)^2+x_1x_2=0\)

\(\Leftrightarrow\left(2m+2\right)^2+m-4=0\)

\(\Leftrightarrow4m^2+9m=0\)

=>m(4m+9)=0

=>m=0 hoặc m=-9/4

a. Với m=6 thì phương trình (1) có dạng 

x^2 - 5x +4= 0

<=> (x-1)(x-4)=0

<=> x=1 hoặc x=4

Vậy m=6 thì phương trình có nghiệm x=1 hoặc x=4

b. Xét \(\text{ Δ}=\left(-5\right)^2-4\cdot1\cdot\left(m-2\right)=33-4m\)

Để (1) có nghiệm phân biệt khi \(m< \dfrac{33}{4}\)

Theo Vi-et ta có: \(x_1x_2=m-2;x_1+x_2=5\)

Để 2 nghiệm phương trình (1) dương khi m>2

Ta có:

\(\dfrac{1}{\sqrt{x_1}}+\dfrac{1}{\sqrt{x_2}}=\dfrac{3}{2}\Leftrightarrow\dfrac{1}{x_1}+\dfrac{1}{x_2}+\dfrac{2}{\sqrt{x_1x_2}}=\dfrac{9}{4}\\ \Leftrightarrow\dfrac{x_1+x_2}{x_1x_2}+\dfrac{2}{\sqrt{x_1x_2}}=\dfrac{9}{4}\\ \Leftrightarrow\dfrac{5}{m-2}+\dfrac{2}{\sqrt{m-2}}=\dfrac{9}{4}\Leftrightarrow20+8\sqrt{m-2}=9\left(m-2\right)\\ \Leftrightarrow\left(\sqrt{m-2}-2\right)\left(9\sqrt{m-2}+10\right)=0\Leftrightarrow\sqrt{m-2}=2\Leftrightarrow m-2=4\Leftrightarrow m=6\left(t.m\right)\)

Đặt \(x+\dfrac{1}{x}=a;y+\dfrac{1}{y}=b\left(\left|a\right|\ge2;\left|b\right|\ge2\right)\)

\(\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=5\\x^3+y^3+\dfrac{1}{x^3}+\dfrac{1}{y^3}=15m-25\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=5\\\left(x^3+\dfrac{1}{x^3}\right)+\left(y^3+\dfrac{1}{y^3}\right)=15m-25\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=5\\\left(x+\dfrac{1}{x}\right)^3-3\left(x+\dfrac{1}{x}\right)+\left(y+\dfrac{1}{y}\right)^3-3\left(y+\dfrac{1}{y}\right)=15m-25\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=5\\\left(x+\dfrac{1}{x}\right)^3+\left(y+\dfrac{1}{y}\right)^3-3\left(x+\dfrac{1}{x}+y+\dfrac{1}{y}\right)=15m-25\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}+y+\dfrac{1}{y}=5\\\left(x+\dfrac{1}{x}\right)^3+\left(y+\dfrac{1}{y}\right)^3=15m-10\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}a+b=5\\a^3+b^3=15m-10\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}a+b=5\\\left(a+b\right)^3-3ab\left(a+b\right)=15m-10\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}a+b=5\\125-15ab=15m-10\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}a+b=5\\ab=9-m\end{matrix}\right.\)

\(\Rightarrow a,b\) là nghiệm của phương trình \(t^2-5t+9-m=0\left(1\right)\)

a, Nếu \(m=3\), phương trình \(\left(1\right)\) trở thành

\(t^2-5t+6=0\)

\(\Leftrightarrow\left[{}\begin{matrix}t=2\\t=3\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}a=2\\b=3\end{matrix}\right.\\\left\{{}\begin{matrix}a=3\\b=2\end{matrix}\right.\end{matrix}\right.\)

TH1: \(\left\{{}\begin{matrix}x+\dfrac{1}{x}=2\\y+\dfrac{1}{y}=3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left(x-1\right)^2=0\\y^2-3y+1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=\dfrac{3\pm\sqrt{5}}{2}\end{matrix}\right.\)

TH2: \(\left\{{}\begin{matrix}x+\dfrac{1}{x}=3\\y+\dfrac{1}{y}=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{3\pm\sqrt{5}}{2}\\y=1\end{matrix}\right.\)

Vậy ...

b, \(\left(1\right)\Leftrightarrow t=\dfrac{5\pm\sqrt{4m-11}}{2}\left(m\ge\dfrac{11}{4}\right)\)

\(\left(1\right)\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{5\pm\sqrt{4m-11}}{2}\\b=\dfrac{5\mp\sqrt{4m-11}}{2}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{x}=\dfrac{5\pm\sqrt{4m-11}}{2}\\y+\dfrac{1}{y}=\dfrac{5\mp\sqrt{4m-11}}{2}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}2x^2-\left(5\pm\sqrt{4m-11}\right)+2=0\left(2\right)\\2y^2-\left(5\mp\sqrt{4m-11}\right)+2=0\end{matrix}\right.\)

Yêu cầu bài toán thỏa mãn khi phương trình \(\left(2\right)\) có nghiệm dương

\(\Leftrightarrow\left\{{}\begin{matrix}\Delta=\left(5\pm\sqrt{4m-11}\right)^2-16\ge0\\\dfrac{5\pm\sqrt{4m-11}}{2}>0\\1>0\end{matrix}\right.\)

\(\Leftrightarrow...\)

Bài 1: 

a) Thay m=3 vào (1), ta được:

\(x^2-4x+3=0\)

a=1; b=-4; c=3

Vì a+b+c=0 nên phương trình có hai nghiệm phân biệt là:

\(x_1=1;x_2=\dfrac{c}{a}=\dfrac{3}{1}=3\)

Bài 2: 

a) Thay m=0 vào (2), ta được:

\(x^2-2x+1=0\)

\(\Leftrightarrow\left(x-1\right)^2=0\)

hay x=1

Phương trình tương đương

\(\left\{{}\begin{matrix}\left(m-1\right)x+2=\left(m+1\right)\left(x-2\right)\\x\ne2\end{matrix}\right.\)

⇔ \(\left\{{}\begin{matrix}\left(m-1\right)x+2=\left(m+1\right)x-2m-2\\x\ne2\end{matrix}\right.\)

⇔ \(\left\{{}\begin{matrix}\left(m-1-m-1\right)x=-2m-4\\x\ne2\end{matrix}\right.\)

⇔ \(\left\{{}\begin{matrix}-2x=-2m-4\\x\ne2\end{matrix}\right.\)

⇔ \(\left\{{}\begin{matrix}x=m+2\\x\ne2\end{matrix}\right.\)

Nếu m = 0 thì phương trình vô nghiệm

Nếu m ≠ 0 thì S = {m + 2}

ĐKXĐ: \(x\ne1;x\ne-2\)\(\Rightarrow\left(2x-m\right)\left(x+2\right)+\left(x+1\right)\left(x-1\right)=3\left(x-1\right)\left(x+2\right)\Leftrightarrow2x^2+4x-mx-2m+x^2-1=3x^2+3x-6\Leftrightarrow3x^2+4x-mx-2m-3x^2-3x=-6\) \(\Leftrightarrow x-mx=2m-6\Leftrightarrow x\left(1-m\right)=2m-6\Leftrightarrow x=\dfrac{2m-6}{1-m}\)

\(\Rightarrow\) Để pt có nghiệm \(\Leftrightarrow m\ne1\)  Vậy...