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hien_vuthithanh
15) (x+4)(x+1)−3x2+5x+2≤6
Đk ⎣⎢⎢⎡x≥217−5x≤2−5−17
\Leftrightarrow x2+5x+4−3x2+5x+2≤6
Đặt x2+5x+2=t(t≥0)
\Rightarrow bpt \Leftrightarrow t2−3t−4≤0 \Leftrightarrow −1≤t≤4
\Leftrightarrow −1≤x2+5x+2≤4
Kết hợp dk \Rightarrow0≤x2+5x+2≤4
\Rightarrow x2+5x+2≤4
\Leftrightarrow x2+5x−14≤0 \Leftrightarrow −7≤x≤2
Kết hợp dk \Rightarrow ⎣⎢⎢⎡−7≤x≤2−5−17217−5≤x≤2
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