Plane and solid geometry . BOOK II THE CIRCLE 276. Def. A circle is a plane closed figure whose boundaryis a curve such that all straight lines to it from a fixed pointwithin are equal. 277. Bef. The curve which formsthe boundary of a circle is called thecircumference. 278. Def. The fixed point withinis called the center, and a line joiningthe center to any point on the circum-ference is called a radius, as QR. 279. From the above definitions and from the definitionof equal figures, § 18, it follows that: (a) All radii of the same circle are equal. (p) All radii of equal circles are equal, (c)
Plane and solid geometry . BOOK II THE CIRCLE 276. Def. A circle is a plane closed figure whose boundaryis a curve such that all straight lines to it from a fixed pointwithin are equal. 277. Bef. The curve which formsthe boundary of a circle is called thecircumference. 278. Def. The fixed point withinis called the center, and a line joiningthe center to any point on the circum-ference is called a radius, as QR. 279. From the above definitions and from the definitionof equal figures, § 18, it follows that: (a) All radii of the same circle are equal. (p) All radii of equal circles are equal, (c) All circles having equal radii are equal. 280. Def. Any portion ofa circumference is called anarc, as DFy FC, etc. 281. Def. A chord is any straight line having its ex-tremities on the circumfer-ence, as DF. 282. Def. A diameter is a chord which passes throughthe center, as BC, 283. Since any diameter is twice a radius, it follows that All diameters of a circle are equal. 113. 114 PLANE GEOMETRY Proposition I. Theorem 284. Every diameter of a circle bisects the circumfer-^ ence aivd the circle, M
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectgeometr, bookyear1912
