d) `3x^2+2x-1=0`
`⇔3x^2+3x-x-1=0`
`⇔3x(x+1)-(x+1)=0`
`⇔(3x-1)(x+1)=0`
`⇔`\(\left[ \begin{array}{l}x=\dfrac{1}{3}\\x=-1\end{array} \right.\)
e)
`x^2-x+1=0`
`⇔x^2-1/2x-1/2x+1/4+3/4=0`
`⇔x(x-1/2)-1/2(x-1/2)=-3/4`
`⇔(x-1/2)^2=-3/4` (vô lý)
`g)` Tương tự
`h)2x^2-5x+7=0`
`⇔2x^2-5/2x-5/2x+25/8+31/8=0`
`⇔2x(x-5/4)-5/2(x-5/4)=-31/8`
`⇔(2x-5/2)(x-5/4)=-31/8`
`⇔2(x-5/4)^2=-31/8` (vô lý)
k) `4x^2-7x+3=0`
`⇔4x^2-4x-3x+3=0`
`⇔4x(x-1)-3(x-1)=0`
`⇔(4x-3)(x-1)=0`
`⇔`\(\left[ \begin{array}{l}x=\dfrac{3}{4}\\x=1\end{array} \right.\)