解: (1)3.14×(18÷2)2 =3.14×81 =254.34(dm2) (2)3.14×(31.4÷3.14÷2)2 =3.14×52 =3.14×25 =78.5(m2) (3)3.14×(6.28÷3.14÷2)2 =3.14×12 =3.14(cm2)
