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a) 13.(23+22)-3.(17+28)
= 13.45 - 3.45
= 45(13-3)
= 45.10 =450
b) -48+48.(-78)+48(-21)
= -48 + 48(-78 - 21)
= -48 + 48.(-99)
= -48 + ( -4752)
= -4800
c) 135.(171-123)-171.(135-123)
= 135.171 - 135.123 - 171.135 + 171.123
= (135.171 - 171.135) - (135.123 - 171.123)
= - 123(135 - 171) = (-123).(-36)= 4428
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![](https://rs.olm.vn/images/avt/0.png?1311)
a)128-(x+56)=15
x+56=128-15
x+56=113
x=113-56
x=57
b)45+(34-x)=67
34-x=67-45=22
x=34-22
x=12
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\(51^{51}=\overline{.....1}\)
\(99^{99}=\left(99^2\right)^{49}\cdot9=\overline{....1}^{49}\cdot9=\overline{....1}\cdot9=\overline{....9}\)
\(22^{22}=\left(22^4\right)^5\cdot2^2=\overline{...6}^5\cdot4=\overline{...6}\cdot4=\overline{....4}\)
\(222^{101}=\left(222^4\right)^2^5\cdot222=\overline{...6}^{25}\cdot222=\overline{....6}\cdot222=\overline{....2}\)
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Quy luật:
00*00=0*0*0*0=0
11*11=1*1*1*1=1
22*22=2*2*2*2=16
33*33=3*3*3*3=81
44*44=4*4*4*4=256
=> 99*99=9*9*9*9=6561
![](https://rs.olm.vn/images/avt/0.png?1311)
78.(-99)+ 99 .(-22)
= -99 .[ 78 + (-22) ]
= -99 .56
= -99 .56
= -5544
Trả lời :
78 . ( - 99 ) + 99 . ( - 22 )
= 78 . ( - 99 ) + ( - 99 ) . 22
= - 99 . ( 78 + 22 )
= - 99 . 100
= - 9900
Hok tốt