tính A=1-2+3-4+5-6+...+1999-2000+2001-2001
B=1-2+3-4+...+1999-2000+2001
1-2+3-4+...+1999-2000+2001=???
A=1-2+3-4+...+1999-2000+2001
C = 1 + ( -2 ) + 3 + ( -4 ) + .... 1999 + ( - 2000 ) + 2001
C = 1 + ( - 2 ) + 3 + ( - 4 ) + ..........+ 1999 + ( - 2000 + 2001 )
Tính tổng:
h) – 1- 2 – 3 – 4 – 5 - … - 1999 – 2000 – 2001 – 2002
-1-2-3-4-5....-1999-2000-2001-2002
1+(-2)+3+(-4)+1999+(-2000)+2001