Question

tính tổng C=-1+3-5+7-9+....-2009+2011-2013

D=2-4+6-8+....+2006-2008+2010-2012

G=1+2-3-4+5+6-7-8+....-111-112+113+114+115

Answer 1

C=(-1+3)+(-5+7)+....+(2011-2013)

  = 2+2+2+...+(-2)

  = 1004+(-2)

  = 1002

Answer 2

D= (2-4)+(6-8)+....+(2010-2012)

  =  -2+-2+-2+...1002+...+-2

  = -502+1002

  = 500

G=(1+2-3-4)+(5+6-7-8)+...+(109+110-111-112)+(113+114+115)

  = -4+-4+-4+...+-4+342

  =-112+342

  = 230