Toán 10

L

lp_qt

$y=\dfrac{x^2-x +1}{x^2+x+1} \iff y.x^2+y.x+y=x^2-x+1 \iff (y-1)x^2+(y+1)x+y-1=0$

phương trình có nghiệm khi $ \Delta=(y+1)^2-4(y-1)^2=(3-y)(3y-2) \ge 0 \iff \dfrac{2}{3} \le y \le 3$
 
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