Thiên An - 2009
[imath](x^2-x)^2+4(x^2-x)+4=0[/imath]
[imath]\iff (x^2-x+2)^2=0[/imath]
[imath]\iff x^2-x+2=0[/imath]
[imath]\iff x^2-x+\dfrac{1}4+\dfrac{7}4=0[/imath]
[imath]\iff (x-\dfrac{1}2)^2+\dfrac{7}4=0[/imath]
[imath](x-\dfrac{1}2)^2\ge 0,\forall x\Rightarrow (x-\dfrac{1}2)^2+\dfrac{7}4\ge \dfrac{7}4>0,\forall x[/imath]
Vậy pt vô nghiệm