N2012 P1 Q11

N2012 P1 Q11

Junior College 2
16 marks

A curve \(C\) has parametric equations \(x=\theta-\sin\theta\), \(y=1-\cos\theta\), where \(0\le\theta\le2\pi\).

  1. Show that \(\frac{\mathrm dy}{\mathrm dx}=\cot\frac12\theta\) and find the gradient of \(C\) at the point where \(\theta=\pi\). What can be said about the tangents to \(C\) as \(\theta\to0\) and \(\theta\to2\pi\)?[5]
  2. Sketch \(C\), showing clearly the features of the curve at the points where \(\theta=0\), \(\pi\) and \(2\pi\).[3]
  3. Without using a calculator, find the exact area of the region bounded by \(C\) and the \(x\)-axis.[5]
  4. A point \(P\) on \(C\) has parameter \(p\), where \(0<p<\frac12\pi\). Show that the normal to \(C\) at \(P\) crosses the \(x\)-axis at the point with coordinates \((p,0)\).[3]

Solution:

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Answer:(i) \(\cot(\theta/2)\), gradient \(0\) at \(\pi\), vertical endpoint tangents. (iii) \(3\pi\). (iv) Normal crosses at \((p,0)\) (shown).

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