1990+1991+1992+……+1999+2000=?

1990+1991+1992+……+1999+2000=? 1990/1990*1991+1990/1991*1992+.+1990/1999*2000 19901×1991\1990+1991×1992\1990.+1999×2000\1990=多少 1/(1/1990+1/1991+1/1992+……1/1999)求整数部分 1992*1999-1991*2000 1991×1999-1990×2000 计算(1990+1992+1994+…+2008)/(1991+1993+1995+…+2009)=? 1992/1993+1991/1993+1990/199+…+3/1993+2/1993+1/1993=? 1985+1987+1989+……+1999/1986+1988+1990+……+2000= 2001-2000-1999+1998+1997-1996+1995-1994-1993+1992+1991-1990+ 1990+1991+…+2001+2002=? 计算：1993+1992-1991-1990+1989+1988-1987-1986+…+5+4-3-2+1=_____