Nếu x = 0 thì `x + x + 1 + x + 2 + x + 3 + ... + x + 2021`
`= 0 + 0 + 1 + 0 + 2 + 0 + 3 + ... + 0 + 2021 `
`= 1 + 2 + 3 + .... + 2021 `( 2021 số hạng )
`= ( 2021 + 1 ) xx 2021 : 2`
`= 2022 xx 2021 : 2 `
`= 2043231`
Nếu x = 1 thì `x + x + 1 + x + 2 + x + 3 + ... + x + 2021`
`= 1 + 1 + 1 + 1 + 2 + 1 + 3 + ... + 1 + 2021`
`= 1 + ( 1 + 1 ) + ( 1 + 2 ) + ( 1 + 3 ) + ... + ( 1 + 2021 )`
`= 1 + 2 + 3 + 4 + ... + 2022 ` ( 2022 số hạng )
`= ( 2022 + 1 ) xx 2022 : 2`
`= 2023 xx 2022 : 2`
`= 2045253`
