Question

Tính nhanh:

a,   1 - 3+ 5 - 7 + ... +2001-2003+2005

b,    1 - 3 + 5 - 7 +...+ 2005 - 2007 + 2009

 

Answer 1

1 - 3 + 5 - 7 + ... + 2001 - 2003 + 2005

= ( 1 - 3 ) + ( 5 - 7 ) + ... + ( 2001 - 2003 ) + 2005

= ( -2 ) + ( -2 ) + ... + ( -2 ) + 2005

= ( -2 ) . 501 + 2005

= ( -1002 ) + 2005

= 1003 

~ Hok tốt ~

Answer 2

1 - 3 + 5 - 7 + ... + 2005 - 2007 + 2009

= ( 1 - 3 ) + ( 5 - 7 ) + ... + ( 2005 - 2007 ) + 2009

= ( -2 ) + ( -2 ) + ... + ( -2 ) + 2009

= ( -2 ) . 502 + 2009

= ( -1004 ) + 2009

= 1005

~ Hok tốt ~

Answer 3

giúp em nốt câu này

1-2+3-4+5-6+...+99-100+101

Answer 4

1 - 2 + 3 - 4 + 5 - 6 + ... + 99 - 100 + 101

= ( 1 - 2 ) + ( 3 - 4 ) + ( 5 - 6 ) + ... + ( 99 - 100 ) + 101

= ( -1 ) + ( -1 ) + ( -1 ) + ... + ( -1 ) + 101

= ( -1 ) . 50 + 101

= ( -50 ) + 101

= 51

~ Hok tốt ~