Combining Windows and Forms Authentication on external website a good idea or not?

I  am creating a website that will be external (i.e. public facing) -
 A) Aswell as the pages that can be accessed anonymously, there will be a number of pages in the website (stored in their own directory) that will only be accessible via Forms Authentication and SQL Server.B) There will also be a number of pages (again stored in their own directory) that will only be used internally  - a user within the domain will be able to logon and access these pages.My question is can I/should I use:
a) Forms Authentication and SQL Server 
               AND
b)Forms Authentication and Active Directory to authenticate the internal users?What would the best course of action to allow external users access the "External Admin" pages and to also allow internal users access the "Internal Admin" pages? All advice appreciated :-)
 
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