The book gave

For , and

I got only

Helmholtz equation: Where

Where is the Spherical Harmonics.

And (1) is the Spherical Bessel function.

Orthogonal properties stated that

For where is finite and :

For and

For and (2)

And (3) where is the j zero of the Bessel function.

Here is my work:

For , and

As the two have different independent variables and from (2),

Using (1), (3)

as is the zero of

I am missing an . Please help

Thanks