Eq: A:1
Multiply both sides of Eq. A.1 by :
Eq: A.2
Subtract Eq. A.2 from Eq. A.1:
Collect terms and simplify:
Eq: A.3
Multiply both sides of Eq. A.3 by :
Eq: A.4
Subtract Eq. A.4 from Eq. A.3 and solve for P to get: