Đáp án+Giải thích các bước giải:
a)
`(x-6)(x^2-4)=0`
`<=> (x-6)(x-2)(x+2)=0`
`<=>` $\begin{cases}x-6-0\\x-2=0\\x+2=0\\\end{cases}$
`<=>` $\begin{cases}x=6\\x=-2\\x=2\\\end{cases}$
b)
`(2x+5)(4x^2-9)=0`
`<=> (2x+5)(2x-3)(2x+3) =0`
`<=>` $\begin{cases}2x+5=0\\2x-3=0\\2x+3=0\\\end{cases}$
`<=>` $\begin{cases}x= \frac{3}{2}\\x=\frac{-5}{2}\\x=\frac{-3}{2}\\\end{cases}$
c)
`(x-2)^2 (x-9)=0`
`<=> (x-2)(x-2)(x-9)=0`
`<=>` $\begin{cases}x=9\\x=2\\\end{cases}$
d)
`x^2=2x`
`<=> x^2-2x=0`
`<=> x(x-2) =0`
`<=>` $\begin{cases}x=0\\x=2\\\end{cases}$
e)
`x^2 -2x+1=4`
`<=> x^2 -2x -3=0`
`<=> x^2 -3x +x -3=0`
`<=> x(x-1)-3(x-1)=0`
`<=> (x-1)(x-3)=0`
`<=>` $\begin{cases}x=1\\x=3\\\end{cases}$
f)
`(x^2+1)(x-1)=0`
`x^2 + 1ge 1 >0 ∀ x`
`=> x-1=0`
`<=> x =1`
g)
`4x^2 + 4x +1 =0`
`<=> (2x+1)^2 =0`
`<=> 2x+1 =0`
`<=> x =-1/2`
h)
`x^2 -5x +6=0`
`<=> x^2 -2x -3x +6 =0`
`<=> x(x-2)-3(x-2)=0`
`<=> (x-3)(x-2)=0`
`<=>` $\begin{cases}x=3\\x=2\\\end{cases}$
i)
`2x^2 + 3x +1=0`
`<=> 2x^2 + 2x + x +1 =0`
`<=> 2x(x+1) + (x+1) =0`
`<=> (2x+1)(x+1)=0`
`<=>` $\begin{cases}x=\frac{-1}{2}\\x=2-1\\end{cases}$
