Question

 

Đề bài là tính nha!

A=1.2+2.3+3.4+4.5+5.6+...+2015.2016

 

Answer 1

3A = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + .... + 2015.2016.2017

3A=2015.2016.2017

A=\(\frac{2015.2016.2017}{3}=.........................\)

Answer 2

A=1.2+2.3+3.4+......+2015.2016

=>3A=1.2.3+2.3.3+3.4.3+....+2015.2016.3

=>3A=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+.....+2015.2016.(2017-2014)

=>3A=1.2.3-0.1.2+2.3.4-1.2.3+3.4.5-2.3.4+.....+2015.2016.2017-2014.2015.2016

=>3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+......+2015.2016.2017-2014.2015.2016

=>3A=2015.2016.2017

=>\(A=\frac{2015.2016.2017}{3}=2731179360\)

Answer 3

2731179360 k mk , mk k lại