1000^2-1001*999
=1000^2-(1000+1)(1000-1)
=1000^2-(1000²-1)
=1000^2-1000²+1
=13*（a-2b)*(1/3a+2/3b)怎么算3*（a-2b)*(1/3a+2/3b) =(a-2b)(a+2b) =a²-4b²祝学习进步，望采纳~~