# Homework Help: Cardoid issue

1. Sep 14, 2010

### iberhammer

A wheel radius a rolls along a line without slipping. The curve traced by a point P that is b units from the center (b < a) is called a curtate cycloid (see figure). Use the angle θ to find a set of parametric equations for this curve.

I went through the book, went to the math lab at my university, and still I cannot find the right solution. I had

x=a(θ-sinθ)
y=a(1-cosθ)

but my tutor just said to replace a and b. I tried that on webassign and still, I received a red mark wrong! I could use some help if anyone could spare any? Thank you all

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2. Sep 14, 2010

### LCKurtz

Of course, your answer can't be correct because it doesn't involve b.

Try thinking of the position vector of the moving point of radius b as the sum of two vectors. The first is the vector from the origin to the center of the circle. The x and y components of that vector only involve a. Then think of the vector from the center of the circle of radius b and angle theta. Write its components in terms of b and theta. Then add the two vectors up.