[面積]99師大地科

[sd030412 (哈比神)]

第四題
A solid ball can be obtained
by revolving the semi-circular region x^2+y^2<=R^2,
x>=0, about the y-axis.
Use the method of disks or cylindrical shells
to find the volume of such a solid ball.

Ans:利用圓盤法則 dv=πx^2dy=π(R^2-y^2)dy,-R<=y<=R
故圓球體積V=  R
            ∫ π(R^2-y^2)dy
              r

我想問的是
為什麼利用圓盤法則是 半徑不是R而是x

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◆ From: 140.138.249.61
→ dali510313:因為是繞y軸旋轉阿0.0方程式變成
→ dali510313:x^2=R^2-y^2
→ dali510313:把圖畫出來你就理解了
→ dali510313:對不起...我想問一下妳的r怎麼來的= ="
→ sd030412:r打錯了是-R
→ sd030412:謝謝囉!!