Question

1*2*3+2*3*4+.........+2011*2012*2013=?

Answer 1

Gọi A = 1.2.3 + 2.3.4 + ................... + 2011.2012.2013

4A = 1.2.3.4 + 2.3.4.4 + ...................... + 2011.2012.2013.4

4A = 1.2.3.4 + 2.3.4.(5 - 1) +..................... + 2011.2012.2013.(2014 - 2010)

4A = 1.2.3.4 + 2.3.4.5 - 1.2.3.4 + .................... + 2011.2012.2013.2014 - 2010.2011.2012.2013

4A = 2011.2012.2013.2014 = ....................................