Question

Tính hợp lí 

a, A=1.2+2.3+3.4+....+2005.2006

Answer 1

A = 1.2 + 2.3 + 3.4 + ... + 2005.2006

3A = 1.2.3 + 2.3.3 + 3.4.3 + ... + 2005.2006.3

3A = 1.2.3 + 2.3.(4 - 1) + 3.4.(5 - 2) + ... + 2005.2006.(2007 - 2004)

3A = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 2005.2006.2007 - 2004.2005.2006

3A = 2005.2006.2007

A = 2690738070

Answer 2

Có A=1.2+2.3+3.4+...+2005.2006

  3A=1.2.3+2.3.3+3.4.3+....+2005.2006.3

3A=1.2.3+2.3.(4-1)+3.4.(5-2)+....+2005.2006.(2007-2004)

3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+....+2005.2006.2007-2004.2005.2006

3A=2005.2006.2007

A=(2005.2006.2007):3

Vậy A=....

Answer 3

A=1.2+2.3+3.4+....+2005.2006

3A = 3( 1.2+2.3+3.4+....+2005.2006)

3A = 1.2.3 + 2.3.3+ 3.4.3+....+2005.2006.3

3A= 1.2.3+ 2.3.(4-1) + 3.4(5-2)+...+2005.2006(2007-2004)

3A= 1.2.3 + 2.3.4  - 1.2.3 + 3.4.5 - 2.3.4 +...+ 2005.2006.2007 - 2004.2005.2006

3A = 2005.2006.2007

3A=8072214210

A= 8072214210;3

A=2690738070

Vậy...

Answer 4

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