Question

设r=√(x^2+y^2+z^2),求gradr,grad(1/r).

Answer 1

gradr={x/√(x^2+y^2+z^2),y/√(x^2+y^2+z^2),z/√(x^2+y^2+z^2)}
gard(1/r)={-x*(x^2+y^2+z^2)^(-3/2),-y*(x^2+y^2+z^2)^(-3/2),-z*(x^2+y^2+z^2)^(-3/2)}