Circles

Question Types
All Questions
On the coordinate plane, there is a figure $\Gamma$ with equation $(x-1)^2 + (y-1)^2 = 101$. Select the correct options.
(1) $\Gamma$ intersects the negative $x$-axis and negative $y$-axis at $(-9, 0)$ and $(0, -9)$ respectively
(2) The point on $\Gamma$ with the maximum $x$-coordinate is $(11, 0)$
(3) The maximum distance from a point on $\Gamma$ to the origin is $\sqrt{2} + \sqrt{101}$
(4) Points on $\Gamma$ in the third quadrant can be expressed in polar coordinates as $[9, \theta]$, where $\pi < \theta < \frac{3}{2}\pi$
(5) After a rotational linear transformation, the figure can still be expressed by a quadratic equation in two variables without an $xy$ term
Suppose $A, B$ are two points on a parabola $\Gamma$ and their connecting line segment passes through the focus $F$ of $\Gamma$. Let the projections of $A, F, B$ onto the directrix of $\Gamma$ be $A', F', B'$ respectively. Select the option equal to $\frac{\overline{AF}}{\overline{A'F'}}$. (Note: This schematic diagram only illustrates the relative positions of the points; the distance relationships between points are not accurate)
(1) $\tan \angle 1$, where $\angle 1 = \angle A'F'A$
(2) $\sin \angle 2$, where $\angle 2 = \angle AF'F$
(3) $\sin \angle 3$, where $\angle 3 = \angle A'AF$
(4) $\cos \angle 4$, where $\angle 4 = \angle F'FB$
(5) $\tan \angle 5$, where $\angle 5 = \angle FF'B$
There is a shooting game with the launcher placed at the origin of a coordinate plane and three circular target disks with radius 1, centered at $(2,2)$, $(4,6)$, and $(8,1)$ respectively. A player selects a positive number $a$ and presses a button. The launcher then fires a laser beam in the direction of point $(1, a)$ (forming a ray). Assume the laser beam can penetrate through the target after hitting it and continue in the original direction (grazing the edge of the disk also counts as a hit). Select the correct options.
(1) The laser beam lies on a line passing through the origin with slope $a$
(2) If $a = \frac{3}{2}$, the laser beam will hit the disk centered at $(4,6)$
(3) The player can hit all three disks with just one laser beam
(4) The player needs to fire at least three laser beams to hit all three disks
(5) If the player fires one laser beam and hits the disk centered at $(8,1)$, then $a \leq \frac{16}{63}$
On the coordinate plane, there is an annular region formed by the intersection of the exterior of the circle $x ^ { 2 } + y ^ { 2 } = 3$ and the interior of the circle $x ^ { 2 } + y ^ { 2 } = 4$ . A person wants to use a straight scanning rod of length 1 to scan a certain region $R$ above the $x$-axis of this annular region. He designs the scanning rod with black and white ends moving respectively on the semicircles $C _ { 1 } : x ^ { 2 } + y ^ { 2 } = 3 ( y \geq 0 )$ and $C _ { 2 } : x ^ { 2 } + y ^ { 2 } = 4 ( y \geq 0 )$ . Initially, the black end of the scanning rod is at point $A ( \sqrt { 3 } , 0 )$ and the white end is at point $B$ on $C _ { 2 }$ . Then the black and white ends move counterclockwise along $C _ { 1 }$ and $C _ { 2 }$ respectively until the white end reaches point $B ^ { \prime } ( - 2,0 )$ on $C _ { 2 }$ , at which point scanning stops.
Let $O$ be the origin. When the scanning rod stops, the positions of the black and white ends are $A ^ { \prime }$ and $B ^ { \prime }$ respectively. In the diagram area of the answer sheet, use hatching to indicate the region $R$ swept by the scanning rod; and in the solution area, find $\cos \angle O A ^ { \prime } B ^ { \prime }$ and the polar coordinates of point $A ^ { \prime }$ . (Non-multiple choice question, 6 points)
On the coordinate plane, there is an annular region formed by the intersection of the exterior of the circle $x ^ { 2 } + y ^ { 2 } = 3$ and the interior of the circle $x ^ { 2 } + y ^ { 2 } = 4$ . A person wants to use a straight scanning rod of length 1 to scan a certain region $R$ above the $x$-axis of this annular region. He designs the scanning rod with black and white ends moving respectively on the semicircles $C _ { 1 } : x ^ { 2 } + y ^ { 2 } = 3 ( y \geq 0 )$ and $C _ { 2 } : x ^ { 2 } + y ^ { 2 } = 4 ( y \geq 0 )$ . Initially, the black end of the scanning rod is at point $A ( \sqrt { 3 } , 0 )$ and the white end is at point $B$ on $C _ { 2 }$ . Then the black and white ends move counterclockwise along $C _ { 1 }$ and $C _ { 2 }$ respectively until the white end reaches point $B ^ { \prime } ( - 2,0 )$ on $C _ { 2 }$ , at which point scanning stops.
(Continuing from Question 19) Let $\Omega$ denote the region swept by the scanning rod in the first quadrant. Find the areas of $\Omega$ and $R$ respectively. (Non-multiple choice question, 6 points)
On a coordinate plane, there is a circle with center $A(a, b)$ that is tangent to both coordinate axes. There is also a point $P(c, c)$, where $a > c > 0$, and it is known that $\overline{PA} = a + c$. Select the correct options.
(1) $a = b$ (2) Point $P$ is on the line $x + y = 0$ (3) Point $P$ is inside the circle (4) $\frac{a + c}{b - c} = \sqrt{2}$ (5) $\frac{a}{c} = 2 + 3\sqrt{2}$
Let $a , b$ be real numbers, and let $O$ be the origin of the coordinate plane. It is known that the graph of the quadratic function $f ( x ) = a x ^ { 2 }$ and the circle $\Omega : x ^ { 2 } + y ^ { 2 } - 3 y + b = 0$ both pass through point $P \left( 1 , \frac { 1 } { 2 } \right)$, and let point $C$ be the center of $\Omega$.
Find the cosine of the angle between vectors $\overrightarrow { C O }$ and $\overrightarrow { C P }$.
Let $a , b$ be real numbers, and let $O$ be the origin of the coordinate plane. It is known that the graph of the quadratic function $f ( x ) = a x ^ { 2 }$ and the circle $\Omega : x ^ { 2 } + y ^ { 2 } - 3 y + b = 0$ both pass through point $P \left( 1 , \frac { 1 } { 2 } \right)$, and let point $C$ be the center of $\Omega$.
Prove that the graph of $y = f ( x )$ and $\Omega$ have a common tangent line at point $P$.
On the coordinate plane, the equation of ellipse $\Gamma$ is $\frac{x^{2}}{a^{2}} + \frac{y^{2}}{6^{2}} = 1$ (where $a$ is a positive real number). If $\Gamma$ is scaled by a factor of 2 in the $x$-axis direction and by a factor of 3 in the $y$-axis direction with the origin $O$ as the center, the resulting new figure passes through the point $(18, 0)$. Which of the following options is a focus of $\Gamma$?
(1) $(0, 3\sqrt{3})$
(2) $(-3\sqrt{5}, 0)$
(3) $(0, 6\sqrt{13})$
(4) $(-3\sqrt{13}, 0)$
(5) $(9, 0)$
On the coordinate plane, let $\Gamma$ be a circle with center at the origin, and $P$ be one of the intersection points of $\Gamma$ and the $x$-axis. It is known that the line passing through $P$ with slope $\frac{1}{2}$ intersects $\Gamma$ at another point $Q$, and $\overline{PQ} = 1$. Then the radius of $\Gamma$ is . (Express as a simplified radical)
In a spatial coordinate system, there is a globe with center at $O ( 0,0,0 )$ and north pole at $N ( 0,0,2 )$. A point $A$ on the sphere has coordinates $\left( \frac { \sqrt { 3 } } { 2 } , \frac { 1 } { 2 } , \sqrt { 3 } \right)$. The point on the equator farthest from point $A$ is point $P$. On the great circle passing through points $A$ and $P$, the length of the minor arc between these two points is (blank). (Express as a fraction in lowest terms)
On the coordinate plane, which of the following equations represents a circle passing through the point $(1,1)$?
(1) $( x - 1 ) ^ { 2 } + y ^ { 2 } = 1$
(2) $( x - 1 ) ^ { 2 } + ( y - 1 ) ^ { 2 } = 1$
(3) $3 ( x - 1 ) ^ { 2 } + y ^ { 2 } = 1$
(4) $x ^ { 2 } + y ^ { 2 } = 1$
(5) $x ^ { 2 } + 3 y = 4$
In the Elements of Geometry, it is stated: "Two distinct points determine a line." In general, three distinct points determine $C_{2}^{3} = 3$ lines; however, if these three points are collinear, only one line is determined. On the coordinate plane, circle $\Gamma_{1}: x^{2} + y^{2} = 4$ intersects the two coordinate axes at 4 points, circle $\Gamma_{2}: x^{2} + y^{2} = 2$ intersects the line $x - y = 0$ at 2 points, and circle $\Gamma_{2}$ intersects the line $x + y = 0$ at 2 points. How many different lines can these 8 points determine?
(1) 12
(2) 16
(3) 20
(4) 24
(5) 28
On the coordinate plane, let $L _ { 1 }$ and $L _ { 2 }$ be two lines passing through point $(3, 1)$ with slopes $m$ and $- m$ respectively, where $m$ is a real number. Let $\Gamma$ be a circle with center at the origin. Given that $\Gamma$ intersects $L _ { 1 }$ at two distinct points $A$ and $B$, and the distance from the center to $L _ { 1 }$ is 1, and $\Gamma$ is tangent to $L _ { 2 }$, then the length of chord $\overline { A B }$ is (express as a fraction in lowest terms).
The line segment joining the points $( 3,3 )$ and ( 7,5 ) is a diameter of a circle. This circle is translated by 3 units in the negative $x$-direction, then reflected in the $x$-axis, and then enlarged by a scale factor of 4 about the centre of the resulting circle.
The equation of the final circle is
A $( x - 2 ) ^ { 2 } + ( y - 4 ) ^ { 2 } = 320$ B $( x - 2 ) ^ { 2 } + ( y + 4 ) ^ { 2 } = 320$ C $( x - 2 ) ^ { 2 } + ( y - 4 ) ^ { 2 } = 80$ D $( x - 2 ) ^ { 2 } + ( y + 4 ) ^ { 2 } = 80$ E $( x - 2 ) ^ { 2 } + ( y - 4 ) ^ { 2 } = 20$ F $( x - 2 ) ^ { 2 } + ( y + 4 ) ^ { 2 } = 20$
Each interior angle of a regular polygon with $n$ sides is $\frac { 3 } { 4 }$ of each interior angle of a second regular polygon with $m$ sides.
How many pairs of positive integers $n$ and $m$ are there for which this statement is true?
A tangent to the circle $x ^ { 2 } + y ^ { 2 } = 144$ passes through the point $( 20,0 )$ and crosses the positive $y$-axis.
What is the value of $y$ at the point where the tangent meets the $y$-axis?
A 12
B 15
C $\frac { 49 } { 3 }$
D 20
E $\frac { 64 } { 3 }$
F $\frac { 80 } { 3 }$
A circle has equation $x ^ { 2 } + y ^ { 2 } - 18 x - 22 y + 178 = 0$
A regular hexagon is drawn inside this circle so that the vertices of the hexagon touch the circle.
What is the area of the hexagon?
A 6
B $6 \sqrt { 3 }$
C 18
D $18 \sqrt { 3 }$
E 36
F $36 \sqrt { 3 }$
G 48
H $48 \sqrt { 3 }$
Find the shortest distance between the two circles with equations:
$$\begin{aligned} & ( x + 2 ) ^ { 2 } + ( y - 3 ) ^ { 2 } = 18 \\ & ( x - 7 ) ^ { 2 } + ( y + 6 ) ^ { 2 } = 2 \end{aligned}$$
A 0
B 4
C 16
D $2 \sqrt { 2 }$
E $5 \sqrt { 2 }$
The circles with equations
$$\begin{aligned} &(x+4)^2 + (y+1)^2 = 64 \quad \text{and} \\ &(x-8)^2 + (y-4)^2 = r^2 \quad \text{where } r > 0 \end{aligned}$$
have exactly one point in common. Find the difference between the two possible values of $r$.
The circle $C_1$ has equation $(x+2)^2 + (y-1)^2 = 3$
The circle $C_2$ has equation $(x-4)^2 + (y-1)^2 = 3$
The straight line $l$ is a tangent to both $C_1$ and $C_2$ and has positive gradient.
The acute angle between $l$ and the $x$-axis is $\theta$
Find the value of $\tan\theta$
A $\frac{1}{2}$
B $2$
C $\frac{\sqrt{2}}{2}$
D $\sqrt{2}$
E $\frac{\sqrt{6}}{2}$
F $\frac{\sqrt{6}}{3}$
G $\frac{\sqrt{3}}{3}$
H $\sqrt{3}$
Two circles have the same radius. The centre of one circle is $( - 2,1 )$. The centre of the other circle is $( 3 , - 2 )$. The circles intersect at two distinct points. What is the equation of the straight line through the two points at which the circles intersect?
A $3 x - 5 y = 4$ B $3 x + 5 y = - 1$ C $5 x - 3 y = - 4$ D $5 x - 3 y = - 1$ E $\quad 5 x - 3 y = 1$ F $5 x - 3 y = 4$ G $5 x + 3 y = 1$
A circle has equation $( x - 9 ) ^ { 2 } + ( y + 2 ) ^ { 2 } = 4$
A square has vertices at $( 1,0 ) , ( 1,2 ) , ( - 1,2 )$ and $( - 1,0 )$.
A straight line bisects both the area of the circle and the area of the square. What is the $x$-coordinate of the point where this straight line meets the $x$-axis?
A 2
B 3
C 4
D 4.5
E 5
F 6
G The straight line is not uniquely determined by the information given, so there is more than one possible point of intersection. $\mathbf { H }$ There is no straight line that bisects both the area of the circle and the area of the square.
A circle has equation
$$x ^ { 2 } + a x + y ^ { 2 } + b y + c = 0$$
where $a , b$ and $c$ are non-zero real constants. Which one of the following is a necessary and sufficient condition for the circle to be tangent to the $y$-axis?
A $a ^ { 2 } = 4 c$
B $b ^ { 2 } = 4 c$
C $\frac { a } { 2 } = \sqrt { \frac { a ^ { 2 } + b ^ { 2 } } { 4 } - c }$
D $\frac { b } { 2 } = \sqrt { \frac { a ^ { 2 } + b ^ { 2 } } { 4 } - c }$ $\mathbf { E } \quad - \frac { a } { 2 } = \sqrt { \frac { a ^ { 2 } + b ^ { 2 } } { 4 } - c }$ $\mathbf { F } \quad - \frac { b } { 2 } = \sqrt { \frac { a ^ { 2 } + b ^ { 2 } } { 4 } - c }$
Which of the following sketches shows the graph of
$$\sin \left( x ^ { 2 } + y ^ { 2 } \right) = \frac { 1 } { 2 }$$
where $x ^ { 2 } + y ^ { 2 } \leq 8 \pi$ ?