Bài 1. Tính hợp lý ( tính nhanh )
1) (–12) +6.(–3)
2) (36 -2020) + (2019 -136) – 27
3) (144 – 97) – (244 – 197)
4) (–24).13 – 24.( –3)
5) 54+55+56+57+58-(64+65+66+67+68)
6) 24(16 – 5) – 16(24 – 5)
7) 47.(23 + 50) – 23.(47 + 50)
8) (-31). 47 + (-31). 52 + (-31)
Bài 2: Tìm số nguyên x, biết:
1)-17-(2x-5)=-6 2) 10-2(4-3x)=-4
3)-12+3(-x+7)=-18 4)-45:[5.(-3-2x)]=3
5) x.(x+3)=0 6) (x-2).(x+4)=0
7) x.(x+1).(x-3)=0
B1
1) (–12) +6.(–3)=-12-18=-30
2) (36 -2020) + (2019 -136) – 27=36-2020+2019-136=-100-1=-101
3) (144 – 97) – (244 – 197)=144-97-244+197=-100+100=0
4) (–24).13 – 24.( –3)=-24(13-3)=-24.10=-240
5) 54+55+56+57+58-(64+65+66+67+68)=54+55+56+57+58-64-65-66-67-68=-10-10-10-10-10=-50
6) 24(16 – 5) – 16(24 – 5)=(384-120)-(384-80)=384-120-384+80=-40
7) 47.(23 + 50) – 23.(47 + 50)=(1081+2350)-(1081+1150)=1081+2350-1081-1150=1200
8) (-31). 47 + (-31). 52 + (-31)=-31(47+52+1)=-31.100=-3100
B2
1)-17-(2x-5)=-6
(=)-2x+5=11
(=)-2x=6
(=)x=-3
2) 10-2(4-3x)=-4
(=)10-8+6x=-4
(=)2+6x=-4
(=)6x=-6
(=)x=-1
3)-12+3(-x+7)=-18
(=)-12-3x+21=-18
(=)9-3x=-18
(=)-3x=-27
(=)x=9
4)-45:[5.(-3-2x)]=3
(=)-45:(-15-10x)=3
(=)-45=3(-15-10x)
(=)-45=-45-30x
(=)0=-30x
(=)x=0
5) x.(x+3)=0
(=)x=0 hoặc x+3=0
+)x=0
+)x+3=0 (=)x=-3
6) (x-2).(x+4)=0
(=)x-2=0 hoặc x+4=0
+)x-2=0 (=)x=2
+)x+4=0(=)x=-4
7) x.(x+1).(x-3)=0
(=)x=0 hoặc x+1=0 hoặc x-3=0
+)x=0
+)x+1=0 (=)x=-1
+)x-3=0 (=)x=3