1、先来画图：RegionPlot3D[x^2+y^2<=z<=1,{x,-1,1},{y,-1,1},{z,-0.5,1.5}
3、如果每一个点的密度都是该点的竖坐标，求这个“物体”的质量：Integrate[z Boole[x^2+y^2<=z<=1], {x,-Infinity,Infinity}, {y,-Infinity,Infinity}, {z,-Infinity,Infinity}]
6、转而尝试球坐标变换：令：{x->r Sin[u] Cos[v],y->r Sin[u] Sin[v],z->r Cos[u]}于是有：dx dy dz->(r^2)Sin[u] dr du dv原题可以化为：Integrate[r^2 Sin[u] Sqrt[x^2+y^2+z^2]/.{x->r Sin[u] Cos[v],y->r Sin[u] Sin[v],z->r Cos[u]},{v,0,2 Pi},{u,0,Pi/2},{r,0,Cos[u]}]
