Let us write  which implies,

(23.12)

Then adding  to both sides of equation (23.12), we obtain the following:

(23.13)

Notice that the conditions

,  and

(23.14)

ensure that,  or .
We can then obtain the following expressions for ,  and ,

2

(23.15)

The conditions as in equation (23.14) are expanded by using the expressions in (23.15), which yield the following results:

(23.16)

(23.17)