The first six books of the Elements of Euclid, and propositions i.-xxi. of book xi

ABCD altitude angle ACB Axiom base bisector bisects Book called centre chord circle circumference circumscribed common const Construct denote described diagonals diameter difference divided draw drawn equal equal angles equiangular equilateral evident Exercises external extremities figure fixed formed four fourth Geometry given circle given line given point greater half Hence inscribed Join less line joining locus magnitudes manner mean meet middle points multiple normal opposite sides pair parallel parallelogram pass perpendicular plane polygon position produced PROP proportional Proposition prove quadrilateral radius ratio rectangle contained regular remaining respectively right angles right line segments sides similar square tangent theorem third touch triangle ABC twice vertex vertical angle volume whole