Đáp án:
`H=2020`
Giải thích các bước giải:
Ta có :
`H=(-2018)-(-2020)-{-1930-45-[-1975-(-2019-2020)-2021]}`
`→H=(-2018)-(-2020)-{-1930-45-[-1975-(-4039)-2021]}`
`→H=(-2018)-(-2020)-(-1930-45+1975-4039+2021)`
`→H=(-2018)-(-2020)-(-1975+1975-4039+2021)`
`→H=(-2018)-(-2020)-(0-4039+2021)`
`→H=(-2018)-(-2020)-(-4039+2021)`
`→H=(-2018)-(-2020)-(-2018)`
`→H=-2018+2020+2018`
`→H=(-2018+2018)+2020`
`→H=0+2020`
`→H=2020`
