Step-by-step explanation:
Assumed Knowledge
Motivation
Content
Radii and chords
Angles in a semicircle
Angles at the centre and circumference
Cyclic quadrilaterals
The alternate segment theorem
Similarity and Circles
Links Forward
Converse of the circle theorems
Coordinate geometry
Calculus
History and Applications
The Euler line
The nine-point circle
Morley’s trisector theorem
Appendix − Converses to the Circle Theorems
Answers to Exercises
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ASSUMED KNOWLEDGE
Introductory plane geometry involving points and lines, parallel lines and transversals, angle sums of triangles and quadrilaterals, and general angle-chasing.
Experience with a logical argument in geometry written as a sequence of steps, each justified by a reason.
Ruler-and-compasses constructions.
The four standard congruence tests and their application to proving properties of and tests for special triangles and quadrilaterals.
The four standard similarity tests and their application.
Trigonometry with triangles.
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MOTIVATION
Most geometry so far has involved triangles and quadrilaterals, which are formed by intervals on lines, and we turn now to the geometry of circles. Lines and circles are the most elementary figures of geometry − a line is the locus of a point moving in a constant direction, and a circle is the locus of a point moving at a constant distance from some fixed point − and all our constructions are done by drawing lines with a straight edge and circles with compasses. Tangents are introduced in this module, and later tangents become the basis of differentiation in calculus.
The theorems of circle geometry are not intuitively obvious to the student, in fact most people are quite surprised by the results when they first see them. They clearly need to be proven carefully, and the cleverness of the methods of proof developed in earlier modules is clearly displayed in this module. The logic becomes more involved − division into cases is often required, and results from different parts of previous geometry modules are often brought together within the one proof. Students traditionally learn a greater respect and appreciation of the methods of mathematics from their study of this imaginative geometric material.
The theoretical importance of circles is reflected in the amazing number and variety of situations in science where circles are used to model physical phenomena. Circles are the first approximation to the orbits of planets and of their moons, to the movement of electrons in an atom, to the motion of a vehicle around a curve in the road, and to the shapes of cyclones and galaxies. Spheres and cylinders are the first approximation of the shape of planets and stars, of the trunks of trees, of an exploding fireball, and of a drop of water, and of manufactured objects such as wires, pipes, ball-bearings, balloons, pies and wheels.
