Theo định lí Viet thì \(\left\{{}\begin{matrix}x_1+x_2=4m\\x_1.x_2=\left(3m-3\right)^2\end{matrix}\right.\)

\(\dfrac{16}{9}.x_1.x_2=\dfrac{16}{9}.\left(3m-3\right)^2\)

⇒ \(\dfrac{16}{9}.x_1.x_2=\left[\dfrac{4}{3}.\left(3m-3\right)\right]^2\)

⇒ \(\dfrac{16}{9}.x_1.x_2=\left(4m-4\right)^2\)

⇒ \(\dfrac{16}{9}.x_1.x_2=\left(x_1+x_2-4\right)^2\)

Đối chiếu ⇒ \(\left\{{}\begin{matrix}a=-4\\b=\dfrac{16}{9}\end{matrix}\right.\)

⇒ \(\dfrac{b}{a}=\dfrac{-4}{9}\)

a: Khi m=5 thì (1) sẽ là: x^2+5x+4=0

=>x=-1; x=-4

b: Sửa đề: Q=x1^2+x2^2-4x1-4x2

Q=(x1+x2)^2-2x1x2-4(x1+x2)

=m^2-2(m-1)-4(-m)

=m^2-2m+2+4m

=m^2+2m+2=(m+1)^2+1>=1

Dấu = xảy ra khi m=-1

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

a: Khi m=1 thì (1) sẽ là:

x^2-4x-5=0

=>x=5 hoặc x=-1

a, Thay m=2 vào pt ta có:
(1)\(\Leftrightarrow2x^2+\left(2.2-1\right)x+2-1=0\)

\(\Leftrightarrow2x^2+3x+1=0\\ \Leftrightarrow\left(2x^2+2x\right)+\left(x+1\right)=0\\ \Leftrightarrow2x\left(x+1\right)+\left(x+1\right)=0\\ \Leftrightarrow\left(2x+1\right)\left(x+1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-1}{2}\\x=-1\end{matrix}\right.\)

b,\(\Delta=\left(2m-1\right)^2-4.2\left(m-1\right)=4m^2-4m+1-8\left(m-1\right)=4m^2-4m+1-8m+8=4m^2-12m+9\)

Để pt có 2 nghiệm thì \(\Delta\ge0\Leftrightarrow4m^2-12m+9\ge0\left(luôn.đúng\right)\)

Theo Vi-ét:\(\left\{{}\begin{matrix}x_1+x_2=\dfrac{1-2m}{2}\\x_1x_2=\dfrac{m-1}{2}\end{matrix}\right.\)

\(4x^2_1+4x^2_2+2x_1x_2=1\\ \Leftrightarrow4\left(x^2_1+x^2_2\right)+2.\dfrac{m-1}{2}=1\\ \Leftrightarrow4\left(x_1+x_2\right)^2-8x_1x_2+m-1=1\\ \Leftrightarrow4.\left(\dfrac{1-2m}{2}\right)^2-8.\dfrac{m-1}{2}+m-2=0\)

\(4.\dfrac{\left(1-2m\right)^2}{4}-4\left(m-1\right)+m-2=0\\ \Leftrightarrow4\left(1-4m+4m^2\right)-4m+4+m-2=0\\ \Leftrightarrow4-16m+16m^2-3m+2=0\\ \Leftrightarrow16m^2-19m+6=0\)

Ta có:\(\Delta=\left(-19\right)^2-4.16.6=361-384=-23< 0\)

Suy ra pt vô nghiệm

1: Ta có: \(\text{Δ}=\left[-2\left(m-1\right)\right]^2-4\cdot\left(m+2\right)\left(3-m\right)\)

\(=\left(2m-2\right)^2+4\left(m+2\right)\left(m-3\right)\)

\(=4m^2-8m+4+4\left(m^2-3m+2m-6\right)\)

\(=4m^2-8m+4+4m^2-4m-24\)

\(=-12m-20\)

Để phương trình có hai nghiệm phân biệt thì Δ>0

\(\Leftrightarrow-12m-20>0\)

\(\Leftrightarrow-12m>20\)

hay \(m< \dfrac{-5}{3}\)

Để phương trình có nghiệm kép thì Δ=0

\(\Leftrightarrow-12m-20=0\)

\(\Leftrightarrow-12m=20\)

hay \(m=\dfrac{-5}{3}\)

Để phương trình vô nghiệm thì Δ<0

\(\Leftrightarrow-12m-20< 0\)

\(\Leftrightarrow-12m< 20\)

hay \(m>\dfrac{-5}{3}\)

2: ĐKXĐ: \(m\ne-2\)

Áp dụng hệ thức Vi-et, ta được:

\(\left\{{}\begin{matrix}x_1+x_2=\dfrac{2\left(m-1\right)}{m+2}=\dfrac{2m-2}{m+2}\\x_1\cdot x_2=\dfrac{3-m}{m+2}\end{matrix}\right.\)

Ta có: \(x_1+x_2=x_1x_2\)

\(\Leftrightarrow\dfrac{2m-2}{m+2}=\dfrac{3-m}{m+2}\)

Suy ra: 2m-2=3-m

\(\Leftrightarrow2m+m=3+2\)

\(\Leftrightarrow3m=5\)

hay \(m=\dfrac{5}{3}\)(thỏa ĐK)

\(\Delta'=\left(m-1\right)^2+m^3-\left(m+1\right)^2=m^3-4m\ge0\) \(\Rightarrow\left[{}\begin{matrix}m\ge2\\-2\le m\le0\end{matrix}\right.\)

Theo hệ thức Viet:  \(\left\{{}\begin{matrix}x_1+x_2=2\left(m-1\right)\\x_1x_2=-m^3+\left(m+1\right)^2\end{matrix}\right.\)

Do \(x_1+x_2\le4\Rightarrow m-1\le2\Rightarrow m\le3\)

\(\Rightarrow\left[{}\begin{matrix}2\le m\le3\\-2\le m\le0\end{matrix}\right.\)

\(P=x_1^3+x_2^3+3x_1x_2\left(x_1+x_2\right)+8x_1x_2\)

\(=\left(x_1+x_2\right)^3+8x_1x_2\)

\(=8\left(m-1\right)^3+8\left[-m^3+\left(m+1\right)^2\right]\)

\(=8\left(5m-2m^2\right)\)

\(P=8\left(5m-2m^2-2+2\right)=16-8\left(m-2\right)\left(2m-1\right)\le16\)

\(P_{max}=16\) khi \(m=2\)

\(P=8\left(5m-2m^2+18-18\right)=8\left(9-2m\right)\left(m+2\right)-144\ge-144\)

\(P_{min}=-144\) khi \(m=-2\)

PT có 2 nghiệm \(\Leftrightarrow\Delta=4\left(m+1\right)^2-4\left(m^2+2\right)\ge0\)

\(\Leftrightarrow4m^2+8m+4-4m^2-8\ge0\\ \Leftrightarrow8m-4\ge0\Leftrightarrow m\ge\dfrac{1}{2}\)

Áp dụng Viét: \(\left\{{}\begin{matrix}x_1+x_2=2\left(m+1\right)\\x_1x_2=m^2+2\end{matrix}\right.\)

\(\Leftrightarrow\left(x_1-x_2\right)^2=\left(x_1+x_2\right)^2-4x_1x_2=8m-4\\ x_1^2+x_2^2=\left(x_1+x_2\right)^2-2x_1x_2=2m^2+8m\)

Ta có \(\left|x_1^4-x_2^4\right|=\left(x_1^2+x_2^2\right)\left|x_1-x_2\right|\left|x_1+x_2\right|\)

\(\Leftrightarrow\left|x_1^4-x_2^4\right|=\left(2m^2+8m\right)\sqrt{\left(x_1-x_2\right)^2}\left|2m+2\right|\\ =8\left(m^2+4m\right)\left|m+1\right|\sqrt{2m-1}\)

Mà \(\left|x_1^4-x_2^4\right|=16m^2+64m=16\left(m^2+4m\right)\)

\(\Leftrightarrow\left(m^2+4m\right)\left|m+1\right|\sqrt{2m-1}-2\left(m^2+4m\right)=0\\ \Leftrightarrow\left(m^2+4m\right)\left(\left|m+1\right|\sqrt{2m-1}-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}m=0\left(ktm\right)\\m=-4\left(ktm\right)\\\left|m+1\right|\sqrt{2m-1}=2\end{matrix}\right.\\ \Leftrightarrow\left(m+1\right)^2\left(2m-1\right)=4\\ \Leftrightarrow2m^3+3m^2-5=0\\ \Leftrightarrow2m^3-2m^2+5m^2-5=0\\ \Leftrightarrow2m^2\left(m-1\right)+5\left(m-1\right)\left(m+1\right)=0\\ \Leftrightarrow\left(m-1\right)\left(2m^2+5m+5\right)=0\\ \Leftrightarrow m=1\left(2m^2+5m+5>0\right)\left(tm\right)\)

Vậy \(m=1\) thỏa mãn đề bài