Bài 30:
a: =>(x-1)(x-2)=0
=>x=1 hoặc x=2
b: =>(x-2)(x-3)=0
=>x=2 hoặc x=3
c: =>(2x-5)(2x-1)=0
=>x=5/2 hoặc x=1/2
d: =>(2x+3)(x+1)=0
=>x=-1 hoặc x=-3/2
a) \(x^2-3x+2=0.\Leftrightarrow\left(x-2\right)\left(x-1\right)=0.\)
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0.\\x-1=0.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2.\\x=1.\end{matrix}\right.\)
b) \(-x^2+5x-6=0.\Leftrightarrow\left(x-3\right)\left(x-2\right)=0.\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=0.\\x-2=0.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3.\\x=2.\end{matrix}\right.\)
c) \(4x^2-12x+5=0.\Leftrightarrow\left(x-\dfrac{5}{2}\right)\left(x-\dfrac{1}{2}\right)=0.\)
\(\Leftrightarrow\left[{}\begin{matrix}x-\dfrac{5}{2}=0.\\x-\dfrac{1}{2}=0.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{2}.\\x=\dfrac{1}{2}.\end{matrix}\right.\)
d) \(2x^2+5x+3=0.\Leftrightarrow\left(x+1\right)\left(x+\dfrac{3}{2}\right)=0.\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=0.\\x+\dfrac{3}{2}=0.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1.\\x=-\dfrac{3}{2}.\end{matrix}\right.\)
