297+298+299+300+301+302+303=( )×( )

问题描述:

297+298+299+300+301+302+303=( )×( )
请解释清楚

(300-3)+(300-2)+(300-1)+300+(300+1)+(300+2)+(300+3)=300x7+(3-3)+(2-2)+(1-1)=300x7=2100