Precalculus: polar curves and signed-radius evidence
Construct complete noncircle polar curves, restrict their traces, and distinguish signed radius from distance and interpolation evidence without calculus.
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Readiness and preparation
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Where does a negative polar radius place a point?
Curve construction must preserve the sign before converting to Cartesian coordinates.
Compare reasoning and find a refresher
The point lies opposite the terminal ray of its angle. Use x=r cos θ and y=r sin θ; the distance from the origin is |r|. For example, r=−1 at θ=π gives (1,0), at distance 1.
Is change in signed radius the same as change in distance?
The two quantities can move in opposite directions when the radius is negative.
Compare reasoning and find a refresher
No. As r decreases from −1 to −2, distance increases from 1 to 2. Keep the angle interval and the scalar quantity explicit; neither change alone measures Cartesian travel length.