Gore, James Howard, 1856-1939 · New York, Longmans, Green, and co. · leaf 38
he other two sides. PROPOSITION XII. THEOREM. 79. TJie sum of the three angles of a triangle is equal to tworight angles. Let ABC be any triangle. To prove that Z A + Z B + /. BCA is equal to two rightangles. From C draw CE parallel to AB. By (63) Z EOF = Z A. By (62) Z BCE = Z. B. But Z BCF = Z… … 80. COR. 1. Equation (a) when expressed in words is: theexterior angle of a triangle is equal to the sum of the two interiorand opposite angles. 81. COR. 2. If two angles of a triangle are given, or merelytheir sum, the third angle can be found by subtracting this sumfrom two right angles. 82. COR.…
Geometry
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