1. 口算。(建议用时3分钟)
$5^2 =$
$8^2 =$
$0.3^2 =$
$0.9^2 =$
$1.1^2 =$
$( \dfrac{3}{4} )^2 =$
$3.14 × 1^2 =$
$3.14 × 2^2 =$
$3.14 × 10^2 =$
$3.14 × 0.1^2 =$
$3.14 × 3^2 =$
$3.14 × ( \dfrac{1}{5} )^2 =$
$3.14 × (6 ÷ 2)^2 =$
$3.14 × (20 ÷ 2)^2 =$
$3.14 × (4 ÷ 2)^2 =$
$3.14 × (0.4 ÷ 2)^2 =$
$3.14 × (2 ÷ 2)^2 =$
$3.14 × (8 ÷ 2)^2 =$

1. 25
64
0.09
0.81
1.21
$\dfrac{9}{16}$
3.14
12.56
314
0.0314
28.26
0.1256
28.26
314
12.56
0.1256
3.14
50.24

2. 求下面各圆的面积。(建议用时2分钟)
(1) $r=1.4\ \mathrm{cm}$
(2) $d=14\ \mathrm{dm}$

2. (1) $3.14 × 1.4^2 = 6.1544(\mathrm{cm}^2)$
(2) $3.14 × ( \dfrac{14}{2} )^2 = 153.86(\mathrm{dm}^2)$

3. 求下面图形的面积。(建议用时2分钟)
(1) ，$d=5\mathrm{dm}$
(2) ，$C=25.12\mathrm{m}$

3. (1) $3.14 × (5 ÷ 2)^2 ÷ 2 = 9.8125(\mathrm{dm}^2)$
(2) $25.12 ÷ 2 ÷ 3.14 = 4(\mathrm{m})$
$3.14 × 4^2 = 50.24(\mathrm{m}^2)$

4. 解决问题。（建议用时3分钟）
鲁班结是一种能够牢牢卡住光滑圆柱体的绳结。小军用一根长24.5 cm的绳子绕一根圆柱形木头练习打鲁班结，绕了2圈还多5.66 cm，这根圆柱形木头的底面面积是多少平方厘米？

4. $(24.5 - 5.66) ÷ 2 = 9.42(\mathrm{cm})$
$9.42 ÷ 2 ÷ 3.14 = 1.5(\mathrm{cm})$
$3.14 × 1.5^2 = 7.065(\mathrm{cm}^2)$