`A=1+(-3)+5+(-7)+... + 2017+(- 2019 )+2021`
`A =1 - 3 + 5 - 7 + ... + 2017 - 2019 + 2021`
`A = ( 1 - 3) + ( 5-7) + ...+ (2017 - 2019) + 2021`
`A =-2 + ( -2)+ ... + (-2) + 2021`
`A = -2. 1010 + 2021`
`A = -1010 + 2021`
`A = 1011`
`B=1+(-2)+3+(-4)+...+(-2020)+2021`
`A = 1- 2 + 3 - 4 + ... +2019 - 2020 +2021`
`A = (1-2) + (3-4) + ... + (2019 - 2020)+ 2021`
`A = -1 + ( -1) + ... + (-1) + 2021`
`A = -1 . 1010 + 2021`
`A = -1001`