( 1 - 1 / 2000 ) * ( 1 - 1 / 1999 ) * ( 1 - 1 / 1998 ) * ( 1 - 1 / 1997 ) * (1- 1/1996
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[1-2-3+4]+........+[1997-1998-1999+2000]+2001
=0+0+....+0+2001
=2001
[1-2-3+4]+........+[1997-1998-1999+2000]+2001
=0+0+....+0+2001
=2001
a) A=1-2-3+4+5-6-7+.....+1996+1997-1998-1999+2000
=(1-2-3+4)+(5-6-7+8)+...+(1997-1998-1999+2000)
=0
b) B=1-3+5-7+....+2001-2003+2005
=(1-3)+(5-7)+...+(2001-2003)+2005
=-2.501+2005
=-1002+2005
=1003
c) C=1-2-3+4+5-6-7+8+.....+1993-1994-1995+1996+1997
=(1-2-3+4)+(5-6-7+8)+...+(1993-1994-1995+1996)+1997
=1997
d) D=1000+998+996+......+10-999-997-995-...-11
=(1000-999)+(998-997)+(996-995)+....+(12-11)+10
=1.495+10
=595
\(D=\dfrac{1}{2000.1999}-\dfrac{1}{1999.1998}-\dfrac{1}{1998.1997}-...-\dfrac{1}{3.2}-\dfrac{1}{2.1}\)
\(D=\dfrac{1}{1999.2000}-\left(\dfrac{1}{1998.1999}+\dfrac{1}{1997.1998}+...+\dfrac{1}{2.3}+\dfrac{1}{1.2}\right)\)\(D=\dfrac{1}{1999.2000}-\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+....+\dfrac{1}{1997.1998}+\dfrac{1}{1998.1999}+\dfrac{1}{1999.2000}\right)\)
\(D=\dfrac{1}{1999.2000}-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+....+\dfrac{1}{1997}-\dfrac{1}{1998}+\dfrac{1}{1998}-\dfrac{1}{1999}+\dfrac{1}{1999}-\dfrac{1}{2000}\right)\)\(D=\dfrac{1}{1999.2000}-\dfrac{1999}{2000}\)
1/2000*1999 - 1/1999*1998 - 1/1998*1997 - ... - 1/2*1
= 1/1999 - 1/2000 - (1/1998 - 1/1999) - (1/1997 - 1/1998) - ... - (1 - 1/2)
= 1/1999 - 1/2000 - 1/1998 + 1/1999 - 1/1997 +1/1998 - .... - 1 + 1/2
= 1/1999 + 1/1999 - 1/2000 - 1/1998 + 1/1998 - 1/1997 +1/1997 - .... - 1/2 +1/2 - 1
= 1/1999 + 1/1999 - 1/2000 - 1
= 2/1999 - 1 - 1/2000
= -1997/1999 - 1/2000
= -2000 - 1997/1997*2000
=-3997/3994000
=
1995/2000
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