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Multiple Choice
Which of the following parametric equations represents a circle of radius centered at the origin, traced counterclockwise as increases from to ?
A
,
B
,
C
,
D
,
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1
Recall that the parametric equations for a circle of radius \( r \) centered at the origin are given by \( x = r \cos(t) \) and \( y = r \sin(t) \), where \( t \) is the parameter representing the angle in radians.
Since the radius is 3, substitute \( r = 3 \) into the general parametric form to get \( x = 3 \cos(t) \) and \( y = 3 \sin(t) \).
The parameter \( t \) should vary from 0 to \( 2\pi \) to trace the entire circle once counterclockwise, because \( \cos(t) \) and \( \sin(t) \) complete one full cycle over this interval.
Check the direction of tracing: as \( t \) increases from 0 to \( 2\pi \), \( (x,y) = (3\cos(t), 3\sin(t)) \) moves counterclockwise around the circle, which matches the problem's requirement.
Verify that the other options do not satisfy the conditions for a circle of radius 3 centered at the origin traced counterclockwise by examining their forms and the behavior of \( x \) and \( y \) as functions of \( t \).