Bài 6:
`a,x^2+4x+3=x^2+x+3x+3`
`=x(x+1)+3(x+1)=(x+1)(x+3)`
`b,2x^2+3x-5=2x^2-2x+5x-5`
`=2x(x-1)+5(x-1)=(x-1)(2x+5)`
`c,16x-5x^2-3=-5x^2+16x-3=-5x^2+15x+x-3`
`=-5x(x-3)+x-3=(x-3)(-5x+1)`
Bài 7:
`a,5x(x-1)=x-1`
`⇔5x(x-1)-(x-1)=0`
`⇔(x-1)(5x-1)=0`
⇔\(\left[ \begin{array}{l}x-1=0\\5x-1=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=1\\5x=1\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=1\\x=\frac{1}{5}\end{array} \right.\)
`b,2(x+5)-x^2-5x=0`
`⇔2(x+5)-x(x+5)=0`
`⇔(x+5)(2-x)=0`
⇔\(\left[ \begin{array}{l}x+5=0\\2-x=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=-5\\x=2\end{array} \right.\)
Bài 8:
`a,x^2-2x-3=0`
`⇔x^2-3x+x-3=0`
`⇔x(x-3)+x-3=0`
`⇔(x-3)(x+1)=0`
⇔\(\left[ \begin{array}{l}x-3=0\\x+1=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=3\\x=-1\end{array} \right.\)
`b,2x^2+5x-3=0`
`⇔2x^2+6x-x-3=0`
`⇔2x(x+3)-(x+3)=0`
`⇔(x+3)(2x-1)=0`
⇔\(\left[ \begin{array}{l}x+3=0\\2x-1=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=-3\\2x=1\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=-3\\x=\frac{1}{2}\end{array} \right.\)
