作者sd030412 (哈比神)
看板trans_math
标题[面积]99师大地科
时间Thu Jun 23 23:16:01 2011
第四题
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:利用圆盘法则 dv=πx^2dy=π(R^2-y^2)dy,-R<=y<=R
故圆球体积V= R
∫ π(R^2-y^2)dy
r
我想问的是
为什麽利用圆盘法则是 半径不是R而是x
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◆ From: 140.138.249.61
1F：→ dali510313:因为是绕y轴旋转阿0.0方程式变成 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:把图画出来你就理解了 111.184.178.34 06/23 23:44
4F：→ dali510313:对不起...我想问一下你的r怎麽来的= =" 111.184.178.34 06/23 23:49
5F：→ sd030412:r打错了是-R 140.138.249.61 06/24 00:05
6F：→ sd030412:谢谢罗!! 140.138.249.61 06/24 00:06