Giải phương trình: $\left\{\begin{matrix} x+y-\sqrt{xy}=8\\ \sqrt{x+1}+\sqrt{y+1}=6 \end{matrix}\right.$
$\left\{\begin{matrix} x+y-\sqrt{xy}=8\\ \sqrt{x+1}+\sqrt{y+1}=6 \end{matrix}\right.$
Started By BysLyl, 23-05-2014 - 20:14
#1
Posted 23-05-2014 - 20:14
#2
Posted 23-05-2014 - 21:08
Giải phương trình: $\left\{\begin{matrix} x+y-\sqrt{xy}=8\\ \sqrt{x+1}+\sqrt{y+1}=6 \end{matrix}\right.$
Cô si:
$(x+1)+9\geq 6\sqrt{x+1}$
$(y+1)+9\geq 6\sqrt{y+1}$
$\Leftrightarrow 6=\sqrt{x+1}+\sqrt{y+1}\leq \frac{x+y+20}{6}\Leftrightarrow x+y\geq 16$
Xét pt (1):
$\sqrt{xy}\leq \frac{x+y}{2}\Leftrightarrow 8=x+y-\sqrt{xy}\geq \frac{x+y}{2}\geq \frac{16}{2}=8$
Dấu = xảy ra khi x = y = 8
- DarkBlood, canhhoang30011999, leduylinh1998 and 4 others like this
#3
Posted 23-05-2014 - 21:11
Traí dấu
tại sao lại trái dấu??
P/s: TL: nhầm
Edited by Trang Luong, 23-05-2014 - 21:17.
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