I don't think I'm the right person of whom to ask that question. ;o)
Also, isn't the Septuagint that version of what Christians call the Old Testament which has all those books in it which Catholics added to the Bible?
I don't think there is a definitive answer to this. It really isn't accurate to speak of "the Septuagint" as one, bound, definitive text.
Indeed. However, doesn't the Septuagint roughly parallel what scholars call 'the Alexandrian canon?' Also, would it be fair to state that if one accepts as canonical the Palestinian canon upon which the Protestant Bible is based then one is forced to admit Matthew's emphasis on the Virgin-Birth of Jesus lacks support from Isaiah? Put simply, wouldn't there be a discrepency between the way Matthew qoutes the verse and the way the verse itself appears in Isaiah?
I don't think there is a definitive answer to this. It really isn't accurate to speak of "the Septuagint" as one, bound, definitive text.
FYI
What is the Septuagint?
The simple answer is that the Septuagint is the Greek translation (from Hebrew) of the Jewish Scriptures, the Christian Old Testament.
Unfortunately, several revisions of this translation were made, and different scholars mean different things when they refer to the 'Septuagint'.
Some mean the original translation of the Torah, which was done in the third century B.C. Some mean the original translation of the entire Old Testament plus Apocrypha, which was done over the next century or so. But so many revisions have been made, that none of these these original translations exist. So some scholars will use 'Sepatuagint' to refer to a particular revision of the translation. But even these can only be reconstructed from what manuscripts we have. So still other scholars will use 'Septuagint' to refer to a particular manuscript of the Septuagint.
So be wary when you read about 'The Septuagint'. It can mean different things to different scholars.Which Septuagint?