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ý bạn là như thế này đúng không ạ:
a/ \(x^2-6x+5=0\)
\(x^2-5x-x+5=0\)
\(x\left(x-5\right)-\left(x-5\right)=0\)
\(\left(x-5\right)\left(x-1\right)=0\)
\(\orbr{\begin{cases}x-5=0\rightarrow x=5\\x-1=0\rightarrow x=1\end{cases}}\)
b/\(2x^2+7x+9=0\)
?!
c/ \(4x^2-7x+3=0\)
\(4x^2-4x-3x+3=0\)
\(4x\left(x-1\right)-3\left(x-1\right)=0\)
\(\left(x-1\right)\left(4x-3\right)=0\)
\(\orbr{\begin{cases}x-1=0\Rightarrow x=1\\4x-3=0\Rightarrow x=\frac{3}{4}\end{cases}}\)
d/ \(2\left(x+5\right)=2x+10\)
-,- mik ko rõ đề ạ, sai thì ibox ạ.Cảm ơn
![](https://rs.olm.vn/images/avt/0.png?1311)
(a) \(9x^2+12x+4=0\)
\(\Leftrightarrow\left(3x+2\right)^2=0\Leftrightarrow3x+2=0\Leftrightarrow x=-\dfrac{3}{2}\)
(b) \(x^2+\dfrac{1}{4}=x\)
\(\Leftrightarrow x^2-x+\dfrac{1}{4}=0\Leftrightarrow\left(x-\dfrac{1}{2}\right)^2=0\Leftrightarrow x-\dfrac{1}{2}=0\Leftrightarrow x=\dfrac{1}{2}\)
(c) \(4-\dfrac{12}{x}+\dfrac{9}{x^2}=0\left(x\ne0\right)\)
\(\Leftrightarrow\left(2-\dfrac{3}{x}\right)^2=0\Leftrightarrow2-\dfrac{3}{x}=0\Leftrightarrow x=\dfrac{3}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a.\left(x^2-2x+1\right)-4=0\\\Leftrightarrow \left(x-1\right)^2-2^2=0\\\Leftrightarrow \left(x-1-2\right)\left(x-1+2\right)=0\\ \Leftrightarrow\left(x-3\right)\left(x+1\right)=0\\\Leftrightarrow \left[{}\begin{matrix}x-3=0\\x+1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3\\x=-1\end{matrix}\right.\)
Vậy tập nghiệm của phương trình trên là \(S=\left\{3;-1\right\}\)
\(b.x^2-x=-2x+2\\\Leftrightarrow x^2-x+2x-2=0\\\Leftrightarrow x\left(x-1\right)+2\left(x-1\right)=0\\\Leftrightarrow \left(x+2\right)\left(x-1\right)=0\\\Leftrightarrow \left[{}\begin{matrix}x+2=0\\x-1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-2\\x=1\end{matrix}\right.\)
Vậy tập nghiệm của phương trình trên là \(S=\left\{-2;1\right\}\)
\(c.4x^2+4x+1=x^2\\ \Leftrightarrow4\left(x^2+x+\frac{1}{4}\right)-x^2=0\\ \Leftrightarrow4\left(x+\frac{1}{2}\right)^2-x^2=0\\ \Leftrightarrow\left[2\left(x+\frac{1}{2}\right)-x\right]\left[2\left(x-\frac{1}{2}\right)+x\right]=0\\ \Leftrightarrow\left[{}\begin{matrix}2\left(x+\frac{1}{2}\right)-x=0\\2\left(x+\frac{1}{2}\right)+x=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x+1-x=0\\2x+1+x=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-1\\x=-\frac{1}{3}\end{matrix}\right.\)
Vậy tập nghiệm của phương trình trên là \(S=\left\{-1;-\frac{1}{3}\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(2x^2-5x^2+6x+13=0\)
\(\Leftrightarrow-3x^2+6x+13=0\)
\(\Leftrightarrow3x^2-6x-13=0\left(1\right)\)
\(\Delta'=9+39=48>0\Rightarrow\sqrt[]{\Delta'}=4\sqrt[]{3}\)
Pt (1) có 2 nghiệm phân biệt là :
\(\left[{}\begin{matrix}x=\dfrac{3+4\sqrt[]{3}}{3}=1+\dfrac{4\sqrt[]{3}}{3}\\x=\dfrac{3-4\sqrt[]{3}}{3}=1-\dfrac{4\sqrt[]{3}}{3}\end{matrix}\right.\)
b) \(x^2-5x=-4\)
\(\Leftrightarrow x^2-5x+4=0\)
\(\Leftrightarrow x^2-x-4x+4=0\)
\(\Leftrightarrow x\left(x-1\right)-4\left(x-1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x-4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x-4=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=4\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(2x^3+5x^2-12x=0\)
\(\Rightarrow x\cdot\left(2x^2+5x-12\right)=0\)
\(\Rightarrow x\cdot\left(2x^2-3x+8x-12\right)=0\)
\(\Rightarrow x\cdot\left[x\cdot\left(2x-3\right)+4\cdot\left(2x-3\right)\right]=0\)
\(\Rightarrow x\cdot\left(2x-3\right)\cdot\left(x+4\right)=0\)
\(\Rightarrow\hept{\begin{cases}x=0\\2x-3=0\\x+4=0\end{cases}}\Rightarrow\hept{\begin{cases}x=0\\x=\frac{3}{2}\\x=-4\end{cases}}\)
\(x^2-5x-24=0\)
\(\Rightarrow x^2+3x-8x-24=0\)
\(\Rightarrow x\cdot\left(x+3\right)-8\cdot\left(x+3\right)=0\)
\(\Rightarrow\left(x+3\right)\cdot\left(x-8\right)=0\)
\(\Rightarrow\hept{\begin{cases}x+3=0\\x-8=0\end{cases}\Rightarrow\hept{\begin{cases}x=-3\\x=8\end{cases}}}\)
\(x^2-6x+8=0\)
\(\Rightarrow x^2-2x-4x+8=0\)
\(\Rightarrow x\cdot\left(x-2\right)-4\cdot\left(x-2\right)=0\)
\(\Rightarrow\left(x-2\right)\cdot\left(x-4\right)=0\)
\(\Rightarrow\hept{\begin{cases}x-2=0\\x-4=0\end{cases}\Rightarrow\hept{\begin{cases}x=2\\x=4\end{cases}}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a,\(2x^2-6x+1=0\)
\(=>x.\left(2x-6\right)=1\)
\(th1:\orbr{\begin{cases}x=1\\2x-6=1\end{cases}=>\orbr{\begin{cases}x=1\\x=\frac{7}{2}\end{cases}}}\)
\(th2:\orbr{\begin{cases}x=-1\\2x-6=-1\end{cases}=>\orbr{\begin{cases}x=-1\\x=\frac{5}{2}\end{cases}}}\)
b,\(4x^2-12x+5=0\)
\(=>x.\left(4x-12\right)=-5\)
\(th1:\orbr{\begin{cases}x=1\\4x-12=-5\end{cases}=>\orbr{\begin{cases}x=1\\x=\frac{7}{4}\end{cases}}}\)
\(th2:\orbr{\begin{cases}x=-1\\4x-12=5\end{cases}=>\orbr{\begin{cases}x=-1\\x=\frac{17}{4}\end{cases}}}\)
\(th3:\orbr{\begin{cases}x=5\\4x-12=-1\end{cases}=>\orbr{\begin{cases}x=5\\x=\frac{11}{4}\end{cases}}}\)
\(th4:\orbr{\begin{cases}x=-5\\4x-12=1\end{cases}=>\orbr{\begin{cases}x=-5\\x=\frac{13}{4}\end{cases}}}\)
\(x^2+6x-16=0\)
Ta có \(\Delta=6^2+4.16=100,\sqrt{\Delta}=10\)
\(\Rightarrow\orbr{\begin{cases}x=\frac{-6+10}{2}=2\\x=\frac{-6-10}{2}=-8\end{cases}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a) (3x - 2)(4x + 5) = 0
<=> 3x - 2 = 0 hoặc 4x + 5 = 0
<=> 3x = 2 hoặc 4x = -5
<=> x = 2/3 hoặc x = -5/4
b) (2,3x - 6,9)(0,1x + 2) = 0
<=> 2,3x - 6,9 = 0 hoặc 0,1x + 2 = 0
<=> 2,3x = 6,9 hoặc 0,1x = -2
<=> x = 3 hoặc x = -20
c) (4x + 2)(x^2 + 1) = 0
<=> 4x + 2 = 0 hoặc x^2 + 1 # 0
<=> 4x = -2
<=> x = -2/4 = -1/2
d) (2x + 7)(x - 5)(5x + 1) = 0
<=> 2x + 7 = 0 hoặc x - 5 = 0 hoặc 5x + 1 = 0
<=> 2x = -7 hoặc x = 5 hoặc 5x = -1
<=> x = -7/2 hoặc x = 5 hoặc x = -1/5
\(x^2-5x-24=0\)
\(x^2+3x-8x-24=0\)
\(x\cdot\left(x+3\right)-8\cdot\left(x+3\right)=0\)
\(\left(x+3\right)\cdot\left(x-8\right)=0\)
\(\hept{\begin{cases}x+3=0\\x-8=0\end{cases}\Rightarrow\hept{\begin{cases}x=-3\\x=8\end{cases}}}\)
\(x^2-6x+8=0\)
\(x^2-2x-4x+8=0\)
\(x\cdot\left(x-2\right)-4\cdot\left(x-2\right)=0\)
\(\left(x-2\right)\cdot\left(x-4\right)=0\)
\(\hept{\begin{cases}x-2=0\\x-4=0\end{cases}\Rightarrow\hept{\begin{cases}x=2\\x=4\end{cases}}}\)
\(2x^2+5x^2-12x=0\)
\(\Leftrightarrow7x^2-12x=0\)
\(\Leftrightarrow x\left(7x-12\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x=0\\7x-12=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=0\\x=\frac{12}{7}\end{cases}}\)