Question

tinh A=1*2+2*3+3*4+4*5+...+2015*2016+2016*2017

Cách giải

Answer 1

A = 1.2+2.3+...+2016.2017

3A=1.2.3 + 2.3.(4-1) + .. + 2016.2017.(2018-2015)

3A = 1.2.3 + 2.3.4 - 1.2.3 + ... + 2016.2017.2018 - 2015.2016.2017

3A = 2016.2017.2018

A = 2016.2017.2018 : 3 

A = 2735245632

Answer 2

3A=1*2*3+2*3*(4-1)+.........+2016*2017.(2018-2015)

3A=1.2.3-1.2.3+2.3.4-2.3.4+.........+2016.2017.3

3A=2016.2017.2018

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