Related questions with answers
Find parametric equations and a parameter interval for the motion of a particle starting at the point (2, 0) and tracing the top half of the circle
four times.
Solutions
VerifiedAt the beginning of the task, we notice that the given equation is the equation of the circle with the center at the origin and the radius .
Since the particle moves on the upper part of the circle, then we will draw only the part of the circle that is above the -axis.

How do we write a circle as a parametric equation?
We can let and since , i.e., .
However, since we only need the top half of the circle, we want to be always positive, therefore, we can modify to be .
Now, at , and at , , that is, on the interval , it traces the top half of the circle once counterclockwise. The second time will be on the interval when it traces the semicircle clockwise from at to at . The third time will be on the interval when it traces the semicircle counterclockwise from at to at . Last but not least, the fourth time will be on the interval when it traces the semicircle clockwise from at to at .
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