作者sd030412 (哈比神)
看板trans_math
標題[面積]99師大地科
時間Thu Jun 23 23:16:01 2011
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
1F：→ dali510313:因為是繞y軸旋轉阿0.0方程式變成 111.184.178.34 06/23 23:44
2F：→ dali510313:x^2=R^2-y^2 111.184.178.34 06/23 23:44
3F：→ dali510313:把圖畫出來你就理解了 111.184.178.34 06/23 23:44
4F：→ dali510313:對不起...我想問一下妳的r怎麼來的= =" 111.184.178.34 06/23 23:49
5F：→ sd030412:r打錯了是-R 140.138.249.61 06/24 00:05
6F：→ sd030412:謝謝囉!! 140.138.249.61 06/24 00:06