A Text-book of Euclid's Elements for the Use of Schools, Book 1

ABCD AC is equal adjacent angles Algebra angle BAC angle equal base BC bisected bisectors centre chord circumference circumscribed circle concyclic Constr Describe a circle diagonal diameter divided equal angles equal in area equiangular Euclid Euclid's exterior angle find the locus given circle given point given straight line given triangle greater Hence hypotenuse inscribed circle isosceles triangle Let ABC line which joins magnitudes meet middle point nine-points circle opposite sides orthocentre par1 parallelogram parm pass pedal triangle perp perpendiculars drawn plane XY polygon produced Proof proportional Proposition Proposition 21 prove quadrilateral radical axis radius rectangle contained rectilineal figure regular polygon right angles segment shew shewn side BC Similarly square straight line drawn tangent Theorem triangle ABC twice the rect vertex vertical angle