... + 12 + (-5) = ((-13) + 13) + ( 12 + 3+(-5)) = 0 +10 =100 .25 0 ,25 b)[ ] [ ]) 42( 12) 64 5() 36( 645−−−−+−+ = 64 5 +(- 36) +(- 64 5)-[ ] 421 2+ =64 5+( -64 5)+(- 36) - 54 = (- 36) +(-54) =-900 ,25 0 ,25 c)( ... 3 45 .2 3 .2 : 2 3 3− + − − = 2 3(5 -2) :2 4 +3-3 =2 3 .2 :2 4 = 2 4 : 2 4=10 ,25 0 ,25 B i 5:à ( 2 ®iÓm): T×m x biÕt: a)75 - x = 83 - ( 35 - 7) 75-x= 51 x = 75-51 x= 24 0 ,25 0 ,25 b) ... x= 24 0 ,25 0 ,25 b) 15 - ( 2x -3) = 6 2x-3 = 15 -6 2x-3=9 2x= 12 x =6 0 ,25 0 ,25 c) 155 12 =+−x 2 1−x =10 1−x= 5 x-1=5 hoÆc x-1 = -5 x =6 hoÆc x=-40 ,25 0 ,25 d) Tìm số tự nhiên x lớn...