练习二1.图左:3.14x(12÷2)2x2+3.14x12x16 = 3.14x36x2+3.14x12x16 =226.08+602.88 =828.96(平方厘米) 图右:3.14x22x2+3.14x2x2x20 =3.14x4x2+3.14x2x2x20 =25.12+251.2 =276.32(平方厘米)2. 20cm=0.2m3.14x0.2x4=2.512(平方米)答:至少需要白铁皮2.512平方米。3.3.14x(6÷2)2+3.14x6x1.5 =3.14x9+3.14x6x1.5 =28.26+28.26 =56.52(平方米)答:抹水泥部分的面积是56.52平方米。4.3.14x22x2+3.14x2x2x8 =3.14x4x2+3.14x2x2x8 =25.12+100.48 =125.6(平方分米)答:至少用铁皮125.6平方分米。5. 花布: 3.14x(18÷2)2x2 =3.14x8 |