a) (-25).13.(-8).4.(-125)
= (-25).4.(-8).(-125).13
= (-100).1000.13
= 1300000
b) -(487+a-789)-(789-487-3a)
= (-487)+(-a)+789+(-789)+487+3a
= (-487)+487+789+(-789)+3a+(-a)
= 0+0+2a
= 2a
c) |2x-7|=11(Có 2 trường hợp)
TH1)2x-7=11
<=>2x=11+7
<=>2x=18
<=>x=18/2
<=>x=9
TH2)2x-7=-11
<=>2x=-11+7
<=>2x=-4
<=>x=-4/2
<=>x=-2
d)3x+12=30+x
<=>3x=x+30-12
<=>3x=x+18
<=>2x+x=x+18
<=>2x=18+x-x
<=>2x=18
<=>x=18/2
<=>x=9
k mình nhé
CHÚC BẠN HỌC GIỎI
(-25 ) . 13 . ( -8 ) . 4 . ( -125 )
= [ -25 . 4 ] . [ -125 . ( -8 ) ] . 13
= -100 . (-1000 ) . 13
= 100 000 . 13
= 1 300 000
| 2x - 7 | = 11
2x = 11 + 7
2x = 18
x = 18 : 2
x = 9
a ) ( - 25 ) . 13 . ( - 8 ) . 4 . ( - 125 )
= [ ( - 25 ) . 4 ] . 13 . [ ( - 8 ) . ( - 125 ) ]
= ( - 100 ) . 13 . 1000
= - 1 300 000