1、(1)5² × 3.14 = 78.5
(2)(1.2 ÷ 2)² × 3.14 = 1.1304
(3)(62.8 ÷ 3.14 ÷ 2)² × 3.14 = 314
2、(1)20² × 3.14 = 1256
(2)(1.57 ÷ 3.14 ÷ 2)² × 3.14 ≅ 0.20
(3)(10 ÷ 2)² × 3.14 = 78.5
3、(1)正方形:(314 ÷ 4)² = 6162.25
圆:(314 ÷ 3.14 ÷ 2)² × 3.14 = 7850
7850 - 6162.25 = 1687.75
围成的圆的面积大,大1687.75平方厘米。
(2)5² - (5 ÷ 2)² × 3.14
= 25 - 19.625
= 5.375