HG 48

D28. Circle [see D3 and A4 on page HG 2]. Additionally, all the other terms associated with circles (diameter, arc, chord, secant, central angle, inscribed angle, congruent angles, . . . ) have the same meaning in HG as in EG. The following are also true in HG.

1. There are 360° in a circle.
2. The line joining the center to a circle to the midpoint of a chord is perpendicular to the chord.
3. A central angle is measured by its intercepted arc.
4. In the same circle or congruent circles, equal central angles subtend equal chords.

T79. The angles inscribed in a semicircle of any given circle are acute.

T80. If A, B, C are three points on a circle with center O, the perpendicular bisectors of the sides of triangle ABC pass through the center of the circle.

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