問題集１p.66 弧度法より 弧 l=rθ=4⋅π3=43πl = r\theta = 4 \cdot \dfrac{\pi}{3} = \dfrac{4}{3}\pil=rθ=4⋅3π=34π cm 面積 S=πr2⋅60°360°=π⋅42⋅16=83π cm2S = \pi r^2 \cdot \dfrac{60°}{360°} = \pi \cdot 4^2 \cdot \dfrac{1}{6} = \dfrac{8}{3}\pi\ cm^2S=πr2⋅360°60°=π⋅42⋅61=38π cm2