Răspuns:
2.)
[tex]a.) \: \: 2019 {}^{2} - 2019 \times 2020 = 2019 \times (2019 - 2020) \\ = 2019 \times ( - 1) = - 2019[/tex]
[tex]b.) \: \: 2019 {}^{2} - 2018 \times 2019 = 2019 \times (2019 - 2018) = 2019 \times 1 = 2019[/tex]
c.) 5+10+15+...+2020 - 5×(1+2+3+...+404) = 5×(1+2+3+..+404) - 5×(1+2+3+...+404)=
(1+2+3+...+404)(5-5) = (1+2+3+...+404)×0 = 0
3.) a.) |-6| = 6 => 3×6 = 18
b.) |-30| = 30 => 30÷5 = 6
