Question

1分之2×5＋1分之5×8＋1分之8×11＋·······＋1分之2003×2006＋1分之2006＋2009

Answer 1

LZ写反了吧、

裂项求和、

原式=1/3*(1/2-1/5+1/5-1/8+……+1/2003-1/2006+1/2006-1/2009)

=1/3(1/2-1/2009)=669/4018