2乘5分之1+5乘8分之1+8乘11分之1=……=

2个回答

2乘5分之1+5乘8分之1+8乘11分之1+……+2006乘2009分之1+2009乘2012分之1
=1/3(1/2-1/5)+1/3(1/5-1/8)+1/3(1/8-1/11)+...+1/3(1/2006-1/2009)+1/3(1/2009-1/2012)
=1/3(1/2-1/2012)
=1/3x1005/2012
=335/2012