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a) 5.2² - 18 : 3
= 5.4 - 18 : 9
= 20 - 2
= 18
b) 17 . 85 + 15 . 17 - 120
= 17 . (85 + 15) - 120
= 17 . 100 - 120
= 1700 - 120
= 1580
c) 2³ . 17 - 2³ . 14
= 8 . 17 - 8 . 14
= 8 . (17 - 14)
= 8 . 3
= 24
a) 5 . 22 – 18 : 32
= 5.4 – 18 : 9
= 20 – 2
= 18
b) 17 . 85 + 15 . 17 – 120
= 17. (85 + 15) – 120
= 17.100 – 120
= 170 – 120
= 50
c) 23 . 17 – 23 . 14
= 23.(17 - 14)
= 23.3
= 8.3
= 24
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\dfrac{9}{23}\left(\dfrac{5}{17}-\dfrac{22}{17}\right)+11+\dfrac{9}{23}=11\)
![](https://rs.olm.vn/images/avt/0.png?1311)
`a)3/5+(-4/9)`
`=3/5-4/9`
`=27/45-20/45`
`=7/45`
`b)3/5+2/5 . 15/8`
`=3/5 + 30/40`
`=3/5+3/4`
`=12/20+15/20`
`=27/20`
`c)7/2 . 8/13 + 8/13 . (-5/2)`
`=8/13 . (7/2 +(-5)/2)`
`=8/13 . 1`
`=8/13`
`d)-5/17 . (-9/23)+9/23 . (-22/17) + 11 9/23`
`=-5/17 . (-9/23) + 9/23 . (-1) . 22/17 + 11 + 9/23`
`=-5/17 . (-9/23) + (-9/23) . 22/17+11+9/23`
`= -9/23 ( -5/17 + 22/17)+11+9/23`
`= - 9/23 . 1+11+9/23`
`=-9/23+11+9/23`
`=(-9/23+9/23)+11`
`=0+11`
`=11`
a: =27/45-20/45=7/45
b: =3/5+30/40
=3/5+3/4
=12/20+15/20
=27/20
c: =8/13(7/2-5/2+1)=8/13*2=16/13
d: =9/23*5/17-9/23*22/17+11+9/23
=-9/23+11+9/23
=11
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 2:
a: \(17-x=3\)
=>\(x=17-3\)
=>x=14(nhận)
b: \(2\cdot\left(x-1\right):3=6\)
=>\(2\left(x-1\right)=6\cdot3=18\)
=>x-1=18/2=9
=>x=9+1=10(nhận)
c: \(x+\left(-2\right)=\left(-11\right)+7\)
=>\(x-2=-4\)
=>\(x=-4+2=-2\left(loại\right)\)
d: \(\left(x-1\right)^2-5=20\)
=>\(\left(x-1\right)^2=25\)
=>\(\left[{}\begin{matrix}x-1=5\\x-1=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\left(nhận\right)\\x=-4\left(loại\right)\end{matrix}\right.\)
Câu 3:
a: Đặt *=a
\(\overline{57a3}⋮9\)
=>\(5+7+a+3⋮9\)
=>\(a+15⋮3\)
mà 0<=a<=9
nên a=3
=>*=a
b: \(A=123\cdot7+8+9\)
123*7 là số lẻ
9 là số lẻ
=>123*7+9 chia hết cho 2
mà 8 chia hết cho 2
nên \(A=123\cdot7+9+8⋮2\)
\(123\cdot7⋮3;9⋮3;8⋮̸3\)
=>\(A=123\cdot7+9+8⋮̸3\)
c: \(B=3\cdot5\cdot7+10^{50}\)
\(=5\cdot3\cdot7+5\cdot5^{49}\cdot2^{49}\)
\(=5\left(3\cdot7+5^{49}\cdot2^{49}\right)⋮5\)
=>B là hợp số
![](https://rs.olm.vn/images/avt/0.png?1311)
13 . ( 23 + 22 ) - 3 . ( 17 + 28 )
= 13 . 45 - 3 . 45
= ( 13 - 3 ) . 45
= 10 . 45
= 450
Tick mình nhé !
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(\dfrac{-7}{12}=\dfrac{-7\cdot5}{12\cdot5}=\dfrac{-35}{60};\dfrac{-1}{-15}=\dfrac{1}{15}=\dfrac{4}{60};\dfrac{-5}{4}=\dfrac{-5\cdot15}{4\cdot15}=-\dfrac{75}{60}\)
\(\dfrac{3}{-5}=\dfrac{-3}{5}=\dfrac{-3\cdot12}{5\cdot12}=-\dfrac{36}{60}\)
mà -75<-36<-35<4
nên \(-\dfrac{75}{60}< -\dfrac{36}{60}< -\dfrac{35}{60}< \dfrac{4}{60}\)
=>\(\dfrac{-5}{4}< \dfrac{3}{-5}< \dfrac{-7}{12}< \dfrac{-1}{-15}\)
b: \(\dfrac{-8}{25}+\dfrac{22}{23}+\dfrac{-17}{25}\)
\(=\left(-\dfrac{8}{25}-\dfrac{17}{25}\right)+\dfrac{22}{23}\)
\(=-1+\dfrac{22}{23}=-\dfrac{1}{23}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 2 :
a, \(x=\dfrac{3}{5}-\dfrac{7}{8}=\dfrac{24-30}{40}=-\dfrac{6}{40}=-\dfrac{3}{20}\)
b, \(2x-1=-2\Leftrightarrow x=-\dfrac{1}{2}\)
13.(23+22)-3.(17+28)
=13.45-3.45
=45.(13-3)
=45.10
=450.