definition
A chord is a segment that joins two points of a circle.

definition
A diameter is a chord that contains the center of the circle.

 

theorem
In a circle, a radius perpendicular to a chord bisects the chord.
Converse:  
In a circle, a radius that bisects a chord is perpendicular to the chord.
Also stated:  
In a circle, the perpendicular bisector of a chord passes through the center of the circle
Extended form:  
In a circle, a diameter perpendicular to a chord bisects the chord and its arc.
 
chord1

chordm1
chord1a

chordm3
Proof:
NewProof
Proof of the converse is left as an exercise.

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theorem
In a circle, or congruent circles, congruent chords are equidistant from the center.
Converse:  
In a circle, or congruent circles, chords equidistant from the center are congruent.
 
chordm5

chord5mmm

chordm5

chordequiGiven

Proof:
newproof2
Proof of the converse is left as an exercise.

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theorem
In a circle, or congruent circles, congruent chords have congruent arcs.
Converse:  
In a circle, or congruent circles, congruent arcs have congruent chords.
 
chord6

chord6m
chord6

chordpf2given
Proof:chordpf23
Proof of the converse is left as an exercise.

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theorem
In a circle, parallel chords intercept congruent arcs
 
chord7

chord7m
chord7

chordparallelgiven
Proof:chordsparallel

 


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