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### Circle

The set of all point in a plane that are equidistant from a given point called the center of the circle. (Page- 651)

### Tangent

A line in the plane of a circle that intersects the circles in exactly 1 point, the point of tangency. (Page- 651)

### Theorem 10.1

In a plane, a line is tangent to a circle if and only if the line is perpendicular to a radius of the circle at its endpoint on the circle. (Page- 653)

### Arc Addition Postulate

The measure of an arc formed by 2 adjacent arcs is the sum of the measures of the 2 arcs. (Page- 660)

### Congruent Arcs

2 arcs are congruent if they have the same measure and they are arcs of the same circle or of congruent circles. (Page- 660)

### Theorem 10.3

In the same circle, or in congruent circles, 2 minor arcs are congruent if and only it their corresponding chords are congruent. (Page- 664)

### Theorem 10.4

If one chord is a perpendicular bisector of another chord, the first chord is a diameter. (Page- 665)

### Theorem 10.5

If a diameter of a circle is perpendicular to a chord, then the diameter bisects the chord and its arc. (Page- 665)

### Theorem 10.6

In then same circle, or in congruent circles, 2 chords are congruent if and only if they are equidistant from the center. (Page- 666)

### Inscribed Angle

An angle whose vertex is on a circle and whose sides contain chords of the circle. (Page- 672)

### Intercepted Arc

The arc that lies in the interior of an inscribed angle and has endpoints of the angle. (Page- 672)

### Measure of an Inscribed Angle Theorem

The measure of an inscribed angle is ½ the measure of its intercepted arc. (Page- 672)

### Theorem 10.8

If 2 inscribed angles of a circle intercept the same arc, then the angles are congruent. (Page- 673)

### Theorem 10.9

If a right triangle is inscribed in a circle, then the hypotenuse is a diameter of the circle. Conversely, if one side of an inscribed triangle is a diameter of the circle, then the triangle is a right triangle and the angle opposite the diameter is the right angle. (Page- 674)

### Theorem 10.10

A quadrilateral can be inscribed in a circle if and only if its opposite angles are supplementary. (Page- 675)

### Theorem 10.11

If a tangent and a chord intersect at a point of a circle, then the measure of each angle formed is ½ the measure it its intercepted arc. (Page- 680)

### Intersecting Lines and Circles

If 2 lines intersect a circle, there are 3 places where the lines can intersect:

1. On the circle

2. Inside the circle

3. Outside the circle

### Angles Inside the Circle Theorem

If 2 chords intersect inside a circle, then the measure of each angle is ½ the sum of the measures of the arcs intercepted by the angle and its vertical angle. (Page- 681)

### Angles Outside Theorem

If a tangent and a secant, 2 tangents, or 2 secants intersect outside of a circle, then the measure of the angle formed is ½ the difference of the measures of the intercepted arcs. (Page- 681)

### Segments of the Chord

When 2 chords intersect in the interior of a circle, each chord is divided into 2 segments that are called segments of the chord. (Page- 689)

### Segments of Chords Theorem

If 2 chords intersect in the interior of a circle, then the product of the lengths of the segments of 1 chord is equal to the product of the lengths of the segments of the other chord. (Page- 689)

### Secant Segment

A segment that contains a chord of a circle, and has exactly one endpoint outside the circle. (Page- 690)

### Segments of Secants Theorem

If 2 segments share the same endpoint outside a circle, then the product of the lengths of 1 secant segment and its external segment equals the product of the lengths of the other secant segment and its external segment. (Page- 690)

### Segments of Secants and Tangents Theorem

If a secant segment and a tangent segment share an endpoint outside a circle, then the product of the lengths of the secant segment and its external segments equals the square of the length of the tangent segment. (Page- 691)

### Locus

The set of all points in a plane that satisfy a given condition or a set of given conditions. (Page- 697)

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