Transformation relationship between spherical coordinate system (r, θ, φ) and rectangular coordinate system (x, y, z);

x=rsinθcosφ

y=rsinθsinφ

z=rcosθ

In the spherical coordinate system, the three line segment elements along the direction of the base vector are:

dl(r)=dr，dl(φ)=rsinθdφ，dl(θ)=rdθ

The bin area of spherical coordinates is:

dS=dl(θ)* dl(φ)=r^2*sinθdθdφ

The volume of the volume element is:

dv=dl(r)*dl(θ)*dl(φ)=r^2*sinθdrdθdφ

This is the formula theorem you need to know in the book, which is very useful for you to do the problem. Now I will explain the question you want to ask with pictures and words ~