Here is a basic lesson in geometrical shapes disguised as entertainment. It aspires to nothing more, and just barely succeeds on its own modest level. The premise is that a busy triangle gets tired of its life and goes to a shapeshifter for an extra angle. Life as a quadrilateral is exciting for a while, but soon the protagonist requires another angle, and--the etceteras take readers through the final two-thirds of the story. Burns (The I Hate Mathematics! Book, Little, 1975, etc.) is wise enough to summarize everything past the hexagon stage. Notes on mathematics for adults working with children appear in the final pages. Newcomer Silveria takes the obvious approach to the illustrator's quandary--how to humanize an abstraction--by adding cute oval eyes and chubby cheeks. His creation comes off like a candidate for the Olympic mascot tryouts; he has a good color sense, and goes full throttle on every page. This installment of the ``Marilyn Burns Brainy Day'' series is static, simplistic, and too long by half--but finding fault with it as a work of art is like looking for character development in a Barney episode. (Picture book. 6-9)