阴影的面积=大半圆面积-小半圆面积
=(10²π/2)-[(10/2)²π/2]
=50π-12.5π
=37.5π
≈37.5×3.14
=117.75平方分米
阴影的周长=大半圆弧长+小半圆的弧长+10
=(2×10π/2)+(10π/2)+10
=10π+5π+10
=15π+10
≈15×3.14+10
=57.1分米
阴影的面积=大半圆面积-小半圆面积
=(10²π/2)-[(10/2)²π/2]
=50π-12.5π
=37.5π
≈37.5×3.14
=117.75平方分米
阴影的周长=大半圆弧长+小半圆的弧长+10
=(2×10π/2)+(10π/2)+10
=10π+5π+10
=15π+10
≈15×3.14+10
=57.1分米