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Questions and Answers

Which of the following is NOT a property of a chord?

  • It is a straight line joining two points on a circle.
  • It touches the circle at only one point. (correct)
  • It divides the circle into two segments.
  • It can pass through the center of the circle.

What term describes the perimeter of a circle?

  • Diameter
  • Arc
  • Radius
  • Circumference (correct)

If a radius of a circle is 5 cm, what is the diameter of the circle?

  • 5 cm
  • 10 cm (correct)
  • 15 cm
  • 2.5 cm

A line is drawn from the center of a circle to the midpoint of a chord. Which statement accurately describes the relationship between the line and the chord?

<p>It is perpendicular to the chord. (B)</p> Signup and view all the answers

What is the relationship between the angle at the center of a circle and the angle at the circumference subtended by the same arc?

<p>The angle at the center is twice the angle at the circumference. (C)</p> Signup and view all the answers

In a cyclic quadrilateral, what is the sum of a pair of opposite angles?

<p>180 degrees (C)</p> Signup and view all the answers

If two tangents are drawn to a circle from the same external point, what can be said about the lengths of the tangents from the external point to the points of tangency?

<p>They are equal in length. (B)</p> Signup and view all the answers

In circle geometry, if an arc subtends an angle of $x$ degrees at the center, and the same arc subtends an angle of $y$ degrees at the circumference, express $x$ in terms of $y$.

<p>$x = 2y$ (D)</p> Signup and view all the answers

Consider a cyclic quadrilateral $ABCD$ inscribed in a circle. If angle $ABC$ is $100$ degrees, what is the measure of angle $ADC$?

<p>80 degrees (D)</p> Signup and view all the answers

Imagine two circles intersecting at points $P$ and $Q$. A line through $P$ intersects the circles at $A$ and $B$, respectively, and a line through $Q$ intersects the circles at $C$ and $D$, respectively. If $AC$ and $BD$ do not intersect inside either circle, and points $A$, $C$, $B$, and $D$ are concyclic, ascertain the relation between $AC$ and $BD$.

<p>They are parallel. (C)</p> Signup and view all the answers

Which of the following terms accurately describes a straight line segment that connects two points on the circumference of a circle?

<p>Chord (B)</p> Signup and view all the answers

According to circle geometry theorems, what is the relationship between a tangent line at any point on a circle and the radius drawn to that same point?

<p>They are perpendicular. (C)</p> Signup and view all the answers

If a line drawn from the center of a circle is perpendicular to a chord, what conclusion can be drawn about the chord?

<p>The chord is bisected. (B)</p> Signup and view all the answers

An arc subtends an angle of $60$ degrees at the circumference of a circle. What is the measure of the angle subtended by the same arc at the center of the circle?

<p>$120$ degrees (D)</p> Signup and view all the answers

Points $A$, $B$, $C$, and $D$ lie on the circumference of a circle. If $\angle ABC = 95^\circ$, what is the measure of $\angle ADC$?

<p>$85^\circ$ (C)</p> Signup and view all the answers

Consider a cyclic quadrilateral $PQRS$. If the exterior angle at vertex $R$ is $70^\circ$, what is the measure of the interior opposite angle at vertex $P$?

<p>$70^\circ$ (A)</p> Signup and view all the answers

From a point $T$ outside a circle, two tangents $TA$ and $TB$ are drawn to the circle, touching it at points $A$ and $B$ respectively. Which of the following statements is always true?

<p>$TA = TB$ (C)</p> Signup and view all the answers

In a circle with center $O$, chord $AB$ subtends $\angle ACB$ at the circumference and $\angle AOB$ at the center. If $\angle ACB = 50^\circ$, and a tangent is drawn at point $A$, forming an angle $\angle CAT$ with chord $AB$. What is the measure of $\angle CAT$?

<p>$50^\circ$ (A)</p> Signup and view all the answers

Consider two equal chords, $PQ$ and $RS$, in a circle with center $O$. If $\angle POQ = 80^\circ$, what is the measure of $\angle ROS$?

<p>$80^\circ$ (D)</p> Signup and view all the answers

Four points $A, B, C, D$ are positioned such that line segment $AB$ subtends equal angles at points $C$ and $D$ on the same side of $AB$. What can be definitively concluded about the points $A, B, C, D$?

<p>They are concyclic. (B)</p> Signup and view all the answers

What distinguishes a diameter from other chords in a circle?

<p>It connects two points on the circumference and passes through the center. (D)</p> Signup and view all the answers

What is the primary conclusion of the Tangent-Chord Theorem?

<p>The angle between a tangent and a chord is equal to the angle in the alternate segment. (C)</p> Signup and view all the answers

If a line segment from the center of a circle bisects a chord that is not a diameter, what can be stated about the line segment and the chord?

<p>The line segment is perpendicular to the chord. (A)</p> Signup and view all the answers

In a cyclic quadrilateral $ABCD$, if $\angle ABC = 75^\circ$, what is the measure of $\angle ADC$?

<p>$105^\circ$ (A)</p> Signup and view all the answers

Two chords, $PQ$ and $RS$, in a circle are equidistant from the center. What can be concluded about their lengths?

<p>$PQ$ and $RS$ are equal in length. (B)</p> Signup and view all the answers

A circle has a radius of 8 cm. From a point 17 cm away from the center, a tangent is drawn to the circle. What is the length of the tangent?

<p>15 cm (C)</p> Signup and view all the answers

In a circle, two parallel chords are drawn on opposite sides of the center. If the chords measure 12 cm and 16 cm and the radius of the circle is 10 cm, what is the distance between the two chords?

<p>14 cm (D)</p> Signup and view all the answers

Consider two circles intersecting at points $A$ and $B$. A line through $A$ intersects the circles at $C$ and $D$, respectively. A line through $B$ intersects the circles at $E$ and $F$, respectively. If $CD$ is parallel to $EF$, what relationship exists between $CE$ and $DF$?

<p>$CE$ is parallel to $DF$. (D)</p> Signup and view all the answers

Two circles intersect at points $P$ and $Q$. Tangents to the circles at point $P$ intersect the circles again at points $A$ and $B$, respectively. What is the relationship between the angle $APB$ and the angle formed by the line segment $PQ$?

<p>$\angle APB$ is supplementary to $\angle PQA + \angle PQB$. (A)</p> Signup and view all the answers

Within a circle of radius $'r'$, two chords of lengths $'a'$ and $'b'$ intersect at right angles. The distance from the center of the circle to the point of intersection of the chords is $'d'$. Identify the correct relationship between $a$, $b$, $r$, and $d$.

<p>$a^2 + b^2 = 4(r^2 - d^2)$ (A)</p> Signup and view all the answers

Which term describes a line that intersects a circle at only one point?

<p>Tangent (B)</p> Signup and view all the answers

What is the defining characteristic of a diameter within a circle?

<p>It is the longest chord and passes through the center. (A)</p> Signup and view all the answers

If a radius of a circle is known, how can the diameter be determined?

<p>Multiply the radius by two. (A)</p> Signup and view all the answers

What term describes a straight line connecting two points on the circumference of a circle?

<p>Chord (D)</p> Signup and view all the answers

If an angle at the center of a circle measures $80$ degrees, what is the measure of the angle at the circumference subtended by the same arc?

<p>$40$ degrees (B)</p> Signup and view all the answers

In a cyclic quadrilateral $ABCD$, if $\angle A = 60^\circ$ and $\angle B = 120^\circ$, what are the measures of $\angle C$ and $\angle D$, respectively?

<p>$120^\circ$ and $60^\circ$ (D)</p> Signup and view all the answers

Given a circle with center $O$, and a tangent $PA$ touching the circle at $A$. If $\angle OAP = x$, what is the value of $x$?

<p>$90^\circ$ (A)</p> Signup and view all the answers

Two chords $AB$ and $CD$ in a circle are equal in length. If they intersect at point $E$ inside the circle, which of the following statements must be true?

<p>$AE = DE$ and $BE = CE$ (B)</p> Signup and view all the answers

In a circle, chords AB and CD intersect at point E. If $AE = 6$, $EB = 4$, and $CE = 3$, what is the length of ED?

<p>8 (A)</p> Signup and view all the answers

If two circles intersect such that the common chord is the diameter of one of the circles, what can be inferred about the relationship between the centers of the two circles and the point(s) of intersection?

<p>The center of the circle with the common chord as diameter lies on the circumference of the other circle. (B)</p> Signup and view all the answers

Flashcards

Arc

A portion of the circumference of a circle.

Chord

A straight line joining the two ends of an arc.

Circumference

The perimeter or boundary line of a circle.

Radius (r)

Any straight line from the center of the circle to a point on the circumference.

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Diameter

A chord that passes through the center of the circle, connecting two points on the circumference.

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Segment

A part of the circle that is cut off by a chord, dividing the circle into two segments.

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Tangent

A straight line that touches the circle at only one point on the circumference.

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Theorem of Pythagoras

In a right-angled triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides: a² + b² = c²

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Angle at the Center Theorem

States that an angle at the center of a circle is twice the angle at the circumference subtended by the same arc.

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Angles Subtended by Same Arc

Angles subtended by a chord of the circle on the same side of the chord are equal.

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Tangent Perpendicular to Radius

A tangent to a circle is perpendicular to the radius drawn to the point of contact, forming a 90-degree angle.

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Line from Center Bisecting Chord

If a line is drawn from the center of a circle perpendicular to a chord, it bisects the chord.

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Cyclic Quadrilateral: Opposite Angles

In a cyclic quadrilateral, the opposite angles are supplementary, meaning they add up to 180 degrees.

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Cyclic Quadrilateral: Exterior Angle

The exterior angle of a cyclic quadrilateral is equal to the interior opposite angle.

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Tangent-Chord Theorem

The angle between a tangent to a circle and a chord drawn from the point of contact is equal to the angle which the chord subtends in the alternate segment.

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Two Tangents From Same Point

Two tangents drawn from the same point outside a circle are equal in length.

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Segment Through Center & Midpoint

The line segment joining the center of a circle and the midpoint of a chord is perpendicular to the chord, forming a right angle.

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Perpendicular Bisector of Chord

The perpendicular bisector of a chord always passes through the center of the circle.

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Perpendicular from Center to Chord

A line segment from the center of a circle that intersects a chord at a right angle will divide the chord into two equal parts.

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Equal Chords Subtend Equal Angles (Center)

If chords in the same circle have equal length, then they create equal angles at the center of the circle.

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Equal Chords Subtend Equal Angles (Circle)

If chords are of equal length, the angles they form on the circle, within corresponding segments, are also equal.

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Chords with Equal Angles

If two chords create equal angles either at a point on the circle, or at the center of the circle, then those chords are equal in length.

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Diameter Subtends Right Angles

Any diameter of a circle, when forming an angle from its endpoints to any point on the circle's circumference, will always create a right angle (90 degrees).

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Points Subtending Equal Angles

If several points along a line segment all subtend the same angle when viewed from another point, those points all lie on the circumference of the same circle.

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Equal Chords, Equal Radii

If chords in different circles, but with equally sized radii, have equal lengths, then the angles they create on their respective circles will be equal.

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Study Notes

  • Euclidean geometry focuses on the properties and relationships of geometric figures in a plane or space, based on a set of axioms and theorems.
  • Circle geometry deals with the specific properties and theorems related to circles.

Terminology

  • Arc: A portion of the circumference of a circle.
  • Chord: A straight line that connects two points on a circle.
  • Circumference: The perimeter or boundary of a circle.
  • Radius (r): The distance from the center of the circle to any point on the circumference.
  • Diameter: A chord that passes through the center of the circle, effectively twice the length of the radius.
  • Segment: An area of the circle enclosed by a chord and the arc it cuts off.
  • Tangent: A line that touches the circle at only one point.

Axioms

  • Theorem of Pythagoras: Describes the relationship between the sides of a right-angled triangle.
  • For a right-angled triangle, with sides of lengths a and b and hypotenuse of length c, the formula is:
    • 𝑎² + 𝑏² = 𝑐²
  • Tangent Perpendicular to Radius: States that at the point where a tangent touches a circle, it forms a right angle with the radius drawn to that point.

Theorems

  • Perpendicular Line from Circle Center Bisects Chord: A line drawn from the center of a circle that is perpendicular to a chord divides the chord into two equal parts.
  • Perpendicular Bisector of Chord Passes Through Circle Center: A line that cuts a chord into two equal parts at a 90-degree angle will always pass through the center of the circle.
  • Angle at the Center is Twice the Angle at the Circumference: The angle formed at the center of a circle by an arc is twice the angle formed at the circumference by the same arc.
  • Angles Subtended by Same Arc: Angles formed by a chord on the same side of the circle's circumference are equal.
  • Opposite Angles of a Cyclic Quadrilateral are Supplementary: In a quadrilateral with all four vertices lying on the circumference of a circle, the angles opposite each other add up to 180 degrees.
  • Exterior Angle of a Cyclic Quadrilateral: The angle formed by extending one side of a cyclic quadrilateral is equal to the angle opposite to the adjacent interior angle.
  • Tangent-Chord Theorem: The angle between a tangent and a chord is equal to the angle in the alternate segment.
  • Two Tangents from the Same Point: Tangents drawn from an external point to a circle are equal in length.

Important Theorems Summary

  • A line from the center of a circle to the midpoint of a chord is perpendicular to the chord.
  • A line from the center of a circle, drawn perpendicular to a chord, bisects the chord.
  • The perpendicular bisector of a chord passes through the center of the circle.
  • The angle at the center of a circle is twice the angle at the circumference subtended by the same arc.
  • Angles subtended by the same arc on the same side are equal.

Corollaries

  • Equal chords in a circle subtend equal angles at the center.
  • Equal chords subtend equal angles on the circle within corresponding segments.
  • Chords are equal if they subtend equal angles at the circumference or at the center of the circle.
  • A diameter always subtends a right angle (90 degrees) at any point on the circle's circumference.
  • In circles of equal radii, equal chords will subtend equal angles.
  • If a line segment connects two points and subtends equal angles on the same side, then the endpoints of the segment and the points where the angles are subtended are concyclic (lie on the same circle).

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