what is the first one about?
It is an ancient Jewish religious work of 50 chapters.
Book of Jubilees
The Book of Jubilees, sometimes called Lesser Genesis (Leptogenesis), is an ancient Jewish religious work of 50 chapters, considered canonical by the Ethiopian Orthodox Church as well as Beta Israel (Ethiopian Jews), where it is known as the "Book of Division" (Ge'ez: መጽሐፈ ኩፋሌ "Mets'hafe Kufale"). 
who lived for many years in the bible Methuselah. has he been mentioned in any other sacred texts? Yes, in the Book of Jubilees and the Rabbinic literature.
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Book of Jubilees [SEP] Introduction
The Book of Jubilees, sometimes called Lesser Genesis (Leptogenesis), is an ancient Jewish religious work of 50 chapters, considered canonical by the Ethiopian Orthodox Church as well as Beta Israel (Ethiopian Jews), where it is known as the "Book of Division" (Ge'ez: መጽሐፈ ኩፋሌ "Mets'hafe Kufale"). "Jubilees" is considered one of the pseudepigrapha by Protestant, Roman Catholic, and Eastern Orthodox Churches. It is also not considered canonical within Judaism outside of Beta Israel. It was well known to Early Christians, as evidenced by the writings of Epiphanius, Justin Martyr, Origen, Diodorus of Tarsus, Isidore of Alexandria, Isidore of Seville, Eutychius of Alexandria, John Malalas, George Syncellus, and George Kedrenos.