Euclid, Libri 1-4

ABCD AC is equal adjacent angles angle ABC angle ACB angle AGH angle BAC angle EDF angle equal base BC bisectors centre circle ABC circles touch circum-circle Constr Construction cyclic quadrilateral Describe a circle diagonals diameter divided draw equal to AC equal to twice equiangular equilateral triangle Euclid exterior angle figure of Prop Find the locus given circle given point given straight line given triangle greater hypotenuse inscribed intersect isosceles triangle Let ABC line joining M.A. Lond meet the circumference middle point opposite sides parallel parallelogram perpendicular point of contact produced Proposition prove quadrilateral figure Radical Axis radii radius rectangle AQ rectangle contained rectilineal figure Reductio ad absurdum regular pentagon rhombus right angles right-angled triangle segment sides equal square on AC straight line drawn tangent theorem triangle ABC twice the rectangle vertical angle