1 求阴影部分的面积。
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)

(1)$3.14×[(\frac{10}{2})^2 - (\frac{8}{2})^2]×\frac{1}{2}=14.13(\mathrm{cm}^2)$
(2)$10÷5=2(\mathrm{cm})$
$3.14×5^2×\frac{1}{2}=39.25(\mathrm{cm}^2)$
$10×5×\frac{1}{2}=25(\mathrm{cm}^2)$
$39.25-25=14.25(\mathrm{cm}^2)$
(3)$3.14×4^2×\frac{1}{4}=12.56(\mathrm{cm}^2)$
(4)$3.14×4^2 - 3.14×(\frac{4}{2})^2=37.68(\mathrm{cm}^2)$
(5)$20×12=240(\mathrm{cm}^2)$
(6)$3.14×4^2×\frac{1}{2} - 3.14×(\frac{4}{2})^2=12.56(\mathrm{cm}^2)$
(7)$8×8 - 3.14×(\frac{8}{2})^2=13.76(\mathrm{dm}^2)$
(8)$S_{梯}=(4+10)×4÷2=28(\mathrm{cm}^2)$
$28 - 3.14×4^2×\frac{1}{4}=15.44(\mathrm{cm}^2)$
(9)$12×12 - 3.14×(\frac{12}{2})^2=30.96(\mathrm{cm}^2)$
(10)$6×3 - 3.14×3^2×\frac{1}{2}=3.87(\mathrm{cm}^2)$
(11)$3.14×4^2×\frac{1}{4}=12.56(\mathrm{cm}^2)$
$3.14×(\frac{4}{2})^2×\frac{1}{2}=6.28(\mathrm{cm}^2)$
$12.56 - 6.28=6.28(\mathrm{cm}^2)$
(12)$3.14×(\frac{4}{2})^2×\frac{1}{2}×4 - 4×4=9.12(\mathrm{cm}^2)$
(13)$4×4÷2=8(\mathrm{cm}^2)$
(14)$3.14×6^2×\frac{1}{4}×2 - 6×6=20.52(\mathrm{cm}^2)$

②如下图，直角梯形的上底是6厘米，下底是9厘米，半圆的直径是6厘米，求阴影部分的面积。

$(6+9)×6÷2=45(\mathrm{cm}^2)$
$3.14×(\frac{6}{2})^2×\frac{1}{2}=14.13(\mathrm{cm}^2)$
$45 - 14.13=30.87(\mathrm{cm}^2)$

3 如下图，涂色部分的面积是多少平方厘米？

$3.14×2^2×\frac{1}{2}=6.28(\mathrm{cm}^2)$