Grade 8Algebra
Evaluate 1+2-3+4+5-6+.....+2005+2006-2007+2008+2009?
Evaluate 1+2-3+4+5-6+.....+2005+2006-2007+2008+2009?
1 Answer
Arun
Dear Nishita
It can be written as
1 + 2 + 3 + 4 + 5 + 6 + 7 +............................. + 2008 + 2009 – [3 + 6 + 9 + 12 + …............+2007]
----------------------------------2009 terms---------------------------- ----------------669 terms--------------
= 2009 (2009 + 1)/2 – 669/2 [3 + 2007]
= 2009 * 1005 – 669 * 1005
= 1005 * 134
= 134170
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