Question

如图1,是一个机器零件,大圆的半径为r+2

Answer 1

(r+2)×(r+2)×π-(r-2)×(r-2)×π

=[(r+2)²-(r-2)²]×π

=[(r+2+r-2)×(r+2-r+2)]×π

=[(2r)×(4)]×π

=8π