toán 10

D

demon311

$\dfrac{5}{x}+\dfrac{5}{1-x} \ge \dfrac{(\sqrt{5}+\sqrt{5})^2}{x+1-x}=20$
$Min y=20$ khi $1-x=x$ \Rightarrow $x=\dfrac{1}{2}$
 
C

congchuaanhsang

Do x $\in$ (0;1) nên x và 1-x dương

Theo Cauchy - Schwarz:

$y=5(\dfrac{1}{x}+\dfrac{1}{1-x})$ \geq $\dfrac{20}{x+1-x}=20$

$y_{min}=20$ \Leftrightarrow $x=\dfrac{1}{2}$
 
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