Math Help - Logistic Discriminant Function

1. Logistic Discriminant Function

Assume P(C2) = eP(C1) (where e is the Euler number ln(e) = 1) and use the logistic discriminant function to derive the explicit expression of P(C1|x)

Where do i start?

Thanks

2. I know P(C2) + P(C1) = 1