Bài 1.
a/ $(-7) . ( 3 - 15 ) . |-18| : 6$
$= (-7) . (-12) . 18 : 6$
$= 84 . 18 : 6$
$= 252.$
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b/ $78 . 27 - 77 . 78 + 22 . (-50)$
$= 78( 27 - 77 ) + 22 . (-50)$
$= 78 . (-50) + 22 . (-50)$
$= ( 78 + 22 ) . (-50)$
$= 100 . (-50)$
$= -5000.$
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c/ $39 - 7 . ( 26 - 30 )²$
$= 39 - 7 . (-4)²$
$= 39 - 112$
$= -73.$
Bài 2.
a/ $31 - ( 14 + 2x ) = (-23)$
$⇔ 31 - 14 - 2x = -23$
$⇔ 2x = -23 - 31 + 14$
$⇔ 2x = -40.$
$⇔ x = -20.$
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b/ $40 - 6x = 4x + 68$
$⇔ 40 - 6x - 4x - 68 = 0$
$⇔ ( 40 - 68 ) - ( 6x - 4x ) = 0$
$⇔ -28 - 2x = 0$
$⇔ 2x = -28$
$⇔ x = -14.$
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c/ $17 + | 5 - x | =21$
$⇔ | 5 - x | = 4$
$⇔$ \(\left[ \begin{array}{l}5-x=4\\5-x=-4\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=1.\\x=9.\end{array} \right.\)
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