用球坐标换元,x^2+y^2+z^2=r^2,dxdydz=r^2*sinφdrdθdφ,积分区域：r：0->1; θ:0->2π; φ:0->π/2
原式=∫∫∫(x^2+y^2+z^2)dxdydz
=∫dθ∫sinφdφ∫r^4dr
=2π*1*1/5
=2/5*π