①2009^2-18*2009+81=2009^2-2*9*2009+9^2=(2009-9)^2=2000^2=4000000 ②3.14*8.75^2-3.14*7.75^2=3.14*(8.75^2-7.75^2)=3.14(8.75+7.75)(8.75-7.75)=3.14*16.5=51.81