Parametrically Defined Circles and Lines

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AP Precalculus › Parametrically Defined Circles and Lines

Questions 1 - 4
1

A sensor sweeps the circle $x=-2+6\cos t,\ y=1+6\sin t$, and a signal line follows $x=4+r,\ y=1+2r$. Find the point(s) where the line intersects the circle defined by the given parametric equations.

No intersection points occur

Intersections at $(4,1)$ and $(0,-7)$

Intersections at $(4,1)$ only

Intersections at $(10,13)$ and $(4,1)$

Explanation

This question tests AP Precalculus skills: understanding parametrically defined circles and lines (focus on algebraic and geometric interpretation). Parametric equations represent geometric figures by defining coordinates as functions of a parameter, often time (t) or distance (r). For this question, the circle has center (-2,1) and radius 6, while the line passes through (4,1) with slope 2. Choice A is correct because substituting x=4+r and y=1+2r into (x+2)²+(y-1)²=36 gives r=0 and r=-4, yielding intersection points (4,1) and (0,-7). Choice C is incorrect as it finds one correct point but miscalculates the second intersection by using the wrong parameter value. To help students: Practice solving quadratic equations that arise from circle-line intersections. Verify solutions by checking that both points satisfy the original circle equation.

2

A skier traces the circle $x=1+4\cos t,\ y=2+4\sin t$, and a tow cable follows $x=5+u,\ y=6-u$. Find the point(s) where the line intersects the circle defined by the given parametric equations.

Intersections at $(1,2)$ and $(9,2)$

Intersections at $(5,6)$ only

Intersections at $(3,4)$ and $(7,0)$

Intersections at $(5,6)$ and $(9,2)$

Explanation

This question tests AP Precalculus skills: understanding parametrically defined circles and lines (focus on algebraic and geometric interpretation). Parametric equations represent geometric figures by defining coordinates as functions of a parameter, often time (t) or distance (u). For this question, the circle has center (1,2) and radius 4, while the line passes through (5,6) with slope -1. Choice A is correct because substituting x=5+u and y=6-u into the circle equation (x-1)²+(y-2)²=16 gives u=0 and u=4, yielding intersection points (5,6) and (9,2). Choice C is incorrect due to an algebraic error in solving the quadratic equation, resulting in wrong parameter values. To help students: Emphasize careful algebraic manipulation when substituting parametric equations. Practice converting between parametric and Cartesian forms, and verify solutions by substituting back into both original equations.

3

A satellite follows the circle $x=-1+3\cos t,\ y=4+3\sin t$, while a scan line follows $x=2+k,\ y=4+2k$. Find the point(s) where the line intersects the circle defined by the given parametric equations.

Intersections at $(5,10)$ and $(2,4)$

Intersections at $(2,4)$ only

Intersections at $(2,4)$ and $(0,0)$

Intersections at $(-4,4)$ and $(2,4)$

Explanation

This question tests AP Precalculus skills: understanding parametrically defined circles and lines (focus on algebraic and geometric interpretation). Parametric equations represent geometric figures by defining coordinates as functions of a parameter, often time (t) or distance (k). For this question, the circle has center (-1,4) and radius 3, while the line passes through (2,4) with slope 2. Choice A is correct because substituting x=2+k and y=4+2k into (x+1)²+(y-4)²=9 gives k=0 and k=-2, yielding intersection points (2,4) and (0,0). Choice C is incorrect as it finds one correct point but uses the wrong parameter value for the second intersection, resulting in a point outside the circle. To help students: Develop systematic approaches to solving circle-line intersection problems. Practice interpreting parameter values geometrically to understand what they represent on the line.

4

A beacon rotates on the circle $x=0+5\cos t,\ y=2+5\sin t$, and a survey line follows $x=5+p,\ y=2+p$. Find the point(s) where the line intersects the circle defined by the given parametric equations.

Intersections at $(5,7)$ and $(0,-3)$

Intersections at $(5,2)$ and $(0,-3)$

Intersections at $(5,2)$ only

Intersections at $(3,4)$ and $(2,5)$

Explanation

This question tests AP Precalculus skills: understanding parametrically defined circles and lines (focus on algebraic and geometric interpretation). Parametric equations represent geometric figures by defining coordinates as functions of a parameter, often time (t) or distance (p). For this question, the circle has center (0,2) and radius 5, while the line passes through (5,2) with slope 1. Choice A is correct because substituting x=5+p and y=2+p into x²+(y-2)²=25 gives p=0 and p=-5, yielding intersection points (5,2) and (0,-3). Choice B is incorrect as it miscalculates the y-coordinate of the first intersection point, likely due to a sign error when evaluating the parametric equation. To help students: Carefully track signs when substituting parameter values back into parametric equations. Verify that calculated points satisfy both the circle and line equations.