Toán 9 xem ho em voi

C

chaugiang81

bài 2.


$A= -x + \sqrt{x} -2 $
$= - (( \sqrt{x})^2 -2.\dfrac{1}{2}.\sqrt{x} + \dfrac{1}{4} )- \dfrac{7}{4} $
$= - (\sqrt{x} - \dfrac{1}{2} )^2 - \dfrac{7}{4} $ \leq $-\dfrac{7}{4}$
vậy $A_{max}= -\dfrac{7}{4}$
dấu = xảy ra khi $\sqrt{x} = \dfrac{1}{2} <=> x= \dfrac{1}{4} $
 
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