Question

c=1*2+2*3+3*4+.....+2017

Answer 1

Nếu đầu bài là: c=1*2+2*3+3*4+.....+2016*2017

Ta có: 3C = 1*2*(3-0) + 2*3*(4-1) + ..... + 2016*2017*(2018 - 2015)

          3C = 1*2*3 - 1*2*3 + 2*3*4 - 2*3*4 + ..... +2016*2017*2018

           3C = 2016*2017*2018   

Answer 2

ban oi cau hoi la 

c= 1*2+2*3+3*4+....+16*17