Bài 2:
1, -2020 + (1534 + 2020)
= -2020 + 1534 + 2020
= 2020 - 2020 + 1534
= 0 - 1534
= -1534
2, (245 - 97) - 245
= 245 - 97 - 245
= 245 - 245 - 97
= 0 - 97
= -97
3, (-145)- (118 - 145)
= -145 - 118 + 145
= 145 - 145 - 118
= 0 - 118
= -118
4, (-36 + 89) - ( 145 + 89 - 36)
= -36 + 89 - 145 - 89 + 36
= (36 - 36) + ( 89 - 89) - 145
= 0 + 0 - 145
= 0 - 145
= -145