[Toán 8]Tìm GTNN

E

eye_smile

$E=\dfrac{x^2}{x-1}=\dfrac{4(x-1)+(x^2-4x+4)}{x-1}=4+\dfrac{(x-2)^2}{x-1} \ge 4$

Dấu = xảy ra \Leftrightarrow $x=2$
 
L

lp_qt

$\dfrac{x^2}{x-1}=\dfrac{(x-1)^2+2(x-1)+1}{x-1}=(x-1)+\dfrac{1}{x-1}+2\ge 2.\sqrt{(x-1).\dfrac{1}{x-1}}+2=4$
 
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