Toán
BÀI 1:Tính
a/(-7).(3-15) ║-18 ║:6
b/78.27-77.78+22.(-50)
c/39-7.926-30) ^2
BÀI 2:Tìm x
31-(14+2x)=(-23)
40-6x=4x+68
17+ ║5-x ║=21
Toán BÀI 1:Tính a/(-7).(3-15) ║-18 ║:6 b/78.27-77.78+22.(-50) c/39-7.926-30) ^2 BÀI 2:Tìm x 31-(14+2x)=(-23) 40-6x=4x+68 17+ ║5-x ║=21
By Madelyn
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/ $31 – ( 14 + 2x ) = (-23)$
$⇔ 31 – 14 – 2x = -23$
$⇔ 2x = -23 – 31 + 14$
$⇔ 2x = -40.$
$⇔ x = -20.$
Vậy…
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b/ $40 – 6x = 4x + 68$
$⇔ 40 – 6x – 4x – 68 = 0$
$⇔ ( 40 – 68 ) – ( 6x – 4x ) = 0$
$⇔ -28 – 2x = 0$
$⇔ 2x = -28$
$⇔ x = -14.$
Vậy…
—
c/ $17 + | 5 – x | =21$
$⇔ | 5 – x | = 4$
$⇔$ \(\left[ \begin{array}{l}5-x=4\\5-x=-4\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=1.\\x=9.\end{array} \right.\)
Vậy…
Giải thích các bước giải:
$\text{Bài 1:}\\a) (-7) . (3 – 15) . |-18|:6\\=(-7) . (-12) . 18 : 6\\=84 . 18 : 6\\= 1512 : 6 = 252\\b) 78 . 27 – 77 . 78 + 22 . (-50)\\=2106 – 6006 + (-1100)\\=(-3900) – 1100 = -5000 \\c) 39 – 7 . (26 – 30)^2\\= 39 – 7 . (-4)^2\\= 39 – 7 . 16 \\= 39 – 112=-73\\ \text{Bài 2:}\\31-(14+2x)=(-23)\\ \Leftrightarrow 14 + 2x = 31 – (-23)\\ \Leftrightarrow 14 + 2x = 54\\ \Leftrightarrow 2x = 40\\ \Leftrightarrow x = 20\\ .\\ 40-6x=4x+68 \\ \Leftrightarrow -6x – 4x = 68 – 40\\ \Leftrightarrow -10x = 28\\ \Leftrightarrow x = -2,8\\.\\ 17 + |5 – x| = 21\\ \Leftrightarrow |5 – x| = 21 – 17\\ \Leftrightarrow |5 – x| = 4\\ \Leftrightarrow\left[ \begin{array}{l}5 – x=4\\5 – x=-4\end{array} \right. \\ \Leftrightarrow \left[ \begin{array}{l}x=1\\x=9\end{array} \right.\\ \text{Vậy x ∈ {1; 9}} $