A = x(x + 2 ) + 2( x - 3 / 2 )
A = x2 + 2x + 2x - 3
A = x2 + 4x - 3
A = x2 + 2 . 2 . x + 22 - 22- 3
A = ( x + 2 )2 - 7\(\ge\)- 7
Dấu " = " xảy ra \(\Leftrightarrow\)x + 2 = 0
\(\Rightarrow\)x = - 2
Min A = - 7 \(\Leftrightarrow\)x = - 2
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