Question

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

B=1-2-3+4+5-6-7+8+...+1993-1994

C=1+2-3-4+5+6-7-8+9+...+2002-2003-2004+2005+2006

 

Answer 1

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

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

A=[(-2)+(-2)+....+(-2)]+2005

Vì từ 1 đến 2003 có: 1002 số hạng => có 501 cặp => có 501 số -2

A=(-2) x 501 +2005

A=-1002+2005

A=1003

Answer 2

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

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

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

A=(-2).501+2005

A=(-1002)+2005

A=1003

B=1-2-3+4+5-6-7+8+...+1993-1994

B=(1-2-3+4)+(5-6-7+8)+....+(1989-1990-1991+1992)+(1993-1994)

B=0+0+...+0+(-1)

B=(-1)

C=1+2-3-4+5+6-7-8+9+...+2002-2003-2004+2005+2006

C=(1+2-3-4)+(5+6-7-8)+....+(2001+2002-2003-2004)+(2005+2006)

C=(-4)+(-4)+....+(-4)+4011

C=(-4).501+4011

C=(-2004)+4011

C=2007

Answer 3

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

A= (-2) + (-2) +....+(-2)  +2005

A= -2. 501 +2005

A= -1002 +2005

A= 1003

B=1-2-3+4+5-6-7+8+...+1993-1994

B= (1-2-3+4) + (5-6-7 +8) +.......+ (1989 - 1990 -1991 +1992)+1993-1994

B= 0 + 0+....+0+ 1993-1994

B= -1

C=1+2-3-4+5+6-7-8+9+...+2002-2003-2004+2005+2006

C= (1+2-3-4) + (5+6-7-8) +.....+(2001+2002 -2003 -2004) +2005+2006

C= -4. 501 + 2005 +2006

C= -2004+2005+2006

C= 2007