Question

(1.2+2.3+......+2017.2018+2018.2019)-(1 mũ2+2 mũ2+.......+2017 mũ2 +2018 mũ 2

Answer 1

(1.2 + 2.3 + 3.4 + ... + 2018.2019) - (1² + 2² + ... + 2018²)

= (1.2 + 2.3 + ... + 2018.2019) - (1.1 + 2.2 + ... + 2018.2018)

= (1.2 + 2.3 + ... + 2018.2019) - [1.(2 - 1) + 2.(3 - 1) + ... + 2018.(2019 - 1)]

= (1.2 + 2.3 + ... + 2018.2019) - (1.2 + 2.3 + ... + 2018.2019 - 1 - 2 - 3 - ... - 2018)

= (1.2 + 2.3 + ... + 2018.2019) - [1.2 + 2.3 + ... + 2018.2019 - (1 + 2 + ... + 2018)]

= (1.2 + 2.3 + ... + 2018.2019) - (1.2 + 2.3 + ... + 2018.2019) + (1 + 2 + 3 + ... + 2018)

= 1 + 2 + ... + 2018 (có : (2018 - 1) : 1 + 1 = 2018 (số))

= (2018 + 1).2018 : 2

= 2037171

Answer 2

cảm ơn nhé

Answer 3

cảm ơn