Toán 8: Tìm GTNN

D

demon311

Đặt $t=|0,5x^2+x| \; (t \ge 0)$

$B=t^2-3t =(t-1,5)^2 -2,25 \ge -2,25 \\
Min \; B =-2,25 \leftrightarrow t=1,5 \\
\leftrightarrow
\left[ \begin{array}{ll}
0,5x^2+x=1,5 \\
0,5x^2+x=-1,5
\end{array} \right.
\leftrightarrow \left[ \begin{array}{ll}
x=1 \\
x=-3
\end{array} \right. $

Hết
 
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