B1:
a)-25+(-42)=-25-42=-67
b)(-17)+5+8+17+(-3)=(-17+17)+(5+8-3)=0+10=10
c)25.2²-(15-18)+(12-19+10)=100+3+3=106
d)120-35+29-242=85-213=-128
B2:
a)100-x=42-(15-7) b)35-3|x|=5.(2³-4)
=>x=100-42-(15-7) =>3|x|=35-20-
=>x=58-8 =>3|x|=15
=>x=50 =>|x|=5
=>x=5 hoac x=-5
c)6.x=-54 d)x-(17-x)=x-14
=>x=-54:6 =>x-17+x=x-14
=>x=-9 =>x+x-x=-14+17
=>x=3
B3:
a)thay so: (-75).(-27).(-8)=2025.(-8)=-16200
b)thay so:1.2.3.4.5.20=(1.2.3).(4.5).20=2400
B4:
tat ca cac U(-2)=-2,-1,1,2
(4)=-4,-2,-1,1,2,4
(13)=-13,-1,1,13
(25)=-25,-5,-1,1,5,25
(1)=-1,1
B5:
a)=> x-3∈U(13) =>x-3∈{-13.-1,1,3} =>x∈{-10,2,4,6}
b) Vi x²-7 chia het cho x²-7
Ma x²+2 chia het cho x²-7
=>(x²+2)-(x²-7) chia het cho x²-7
=>x²+2-x²+7 chia het cho x²-7
=>9 chia het cho x²-7
=>x²-7∈U(9) =>x²-7∈{-9,-3,-1,1,3,9}=>x²∈{-2,4,6,8,10,16} =>x∈{2,4}
