Bài `2:`
`a) 2 +(-15) = -13`
`b) 2.(-3) -7 =-6-7 = -13`
`c) 5.(28-4) +(-1)^2 = 5.24 + 1 =120 +1 =121`
`d) 3.|-4| + 6:(-2) = 3.4 -3 = 12 -3 =9`
Bài `3:`
`a) x+8=13`
`=> x = 13-8`
`=> x= 5`
`b) 4-x=8`
`=> x = 4-8`
`=> x=-4`
`c) 13-(2x+11)= 2`
`=> 13 -2x - 11 =2`
`=> -2x = 2-13 +11`
`=> -2x = 0`
`=> x=0`
`d) (x+1).(x-2)=0`
`=> x+1=0` hoặc `x-2=0`
`+) x+1=0 => x=0-1 => x =-1`
`+) x -2 =0 <=> x =0+2 => x =2`
Vậy ` x\in{-1;2}`
