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P3 Topic 2: Coordinate geometry in the (x, y) plane
extended problem P3.1 backmore
(a) Observe the curve x = r cos t, y = r sin t. Click on "Equalize axes" to get an accurate display of the shape of the curve. Try various values of r. Describe what happens. What is the cartesian equivalent?
(b) Extend to x =a + r cos t, y =b + r sin t for various values of the constants a and b.
Describe fully the resulting curve, noting particularly the significance of a, b and r.
What is the cartesian equivalent now?
What are the general charactersitics when
(i) a = r
(ii) b = r ?
Prove your answers.
(c) Return to the case x = r cos t, y = r sin t. Suppose we wish to join up two points on this curve with a straight line. Investigate the case when the points have parameters p and q subject to the constraint that p+q = 1.
Do the same for other values of p and q with p+q = 1. What do you notice? Prove your answer.
(d) What if p+q = m, where m is some other number? Does a similar effect occur? What is the gradient of the chords when p+q = m?

x = r cos t, y = r sin t


x = r cos t, y = r sin t, straight line


x = r cos t, y = r sin t, straight line where p+q = m


Summary
This problem is adapted from "Exploring Maths with Computers" by Aydin Önaç, The Chase, Malvern
JavaMath interactive graphs Based on free Java applets from JavaMath