. The Decorator's assistant. 181 IHensiiratiort of Supetticeg, {Continued from page 174.) PROBLEM XI. To find the length of an arc A b, the circumference a d b a or the diameter d b beinggiven. A ^^ ^ B. 1. When the circumference is given, makethe following proportion—as 360 degrees is tothe number of degrees in the arc, so is the circumference to the length of the arc. 2. When the diameter is given, first find thecircumference by the last problem, and thenthe length of the arc as above. Example 1.—The arc ab being 70 degrees,and the circumference a d b a 60 feet, whatwill be the length of the
. The Decorator's assistant. 181 IHensiiratiort of Supetticeg, {Continued from page 174.) PROBLEM XI. To find the length of an arc A b, the circumference a d b a or the diameter d b beinggiven. A ^^ ^ B. 1. When the circumference is given, makethe following proportion—as 360 degrees is tothe number of degrees in the arc, so is the circumference to the length of the arc. 2. When the diameter is given, first find thecircumference by the last problem, and thenthe length of the arc as above. Example 1.—The arc ab being 70 degrees,and the circumference a d b a 60 feet, whatwill be the length of the arc a b ? 360 : 70 : : 60 : arc a !6) 4200 60) 700 feet = arc A B. Example 2.—The arc being 80 degrees andthe diameter 180 feet, what will be the lengthof the arc ? = circumf.: : : : arc. 360 : 6) 60) = 125 ft. 8 in. nearly = arc. PROBLEM XII. To find the area of a circle. 1. When the diameter is given, multiply thesquare of the diameter by .7854, and the pro-duct will be the area. 2. When the circumference and diameterboth are given, multiply half the circumferenceby half the diameter, and the produce will
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