...therefore equal. 76. Exercises. 1. Prove by means of the annexed diagram, in which DE is parallel to AC, that the sum of the three angles of a triangle is equal to two right angles. 2. The sum of the three straight lines drawn from any point within a triangle to the vertices...

...Thales can be drawn from the preceding notices. First inference. — Thales must have known the theorem that the sum of the three angles of a triangle is equal to two right angles. Pamphila, in [<f], refers to the discovery of the property of a circle that all triangles described...

...a point to a straight line make equal acute angles with that line. PROPOSITION XXL THEOREM. 98. The sum of the three angles of a triangle is equal to two right angles. BE C Let ABC be a triangle. We are to prove ZB + ZB CA + ZA = two rt. A Draw CE II to AB, and...

...point to a straight line make equal acute angles with that line. PROPOSITION XXI. THEOREM. 98. The sum of the three angles of a triangle is equal to two righd angles. BE C Let ABC be a triangle. We are to prove Z. B + Z. BCA + Z. A = two rt. A. Draw CE...

...scientific accuracy is proverbial. It is susceptible of definite proof that two and two make four; that the, sum of the three angles of a triangle is equal to two right angles and nothing else. There need never be any question as to what will result when carbon burns...

...on. Hence, the proposition must be universally true. 466. In Geometry, we have the proposition : TJie sum of the three angles of a triangle is equal to two right angles. We find it to be true in one case ; then in another, etc. Hence, we conclude the proposition...

...best policy. 15. Education cannot be effected by mere class-room instruction or lecturing. 16. The sum of the three angles of a triangle is equal to two right angles. 17. Two straight lines cannot inclose a space. 18. The earth is between 93,000,000 and 94,000,000...

...opposite sides of a straight line which cuts two parallels ........ 36 These angles are equal 37 64. The sum of the three angles of a triangle is equal to two right angles 37 68. The exterior angle of a triangle is equal to the sum of its two interior opposite angles...

...perpendicular, each to each, they are either equal or supplementary. PROPOSITION XXI. THEOREM. 98. The sum of the three angles of a triangle is equal to two right angles. BE С Let AB С be a triangle. We are to prove ¿ B + ZB С A + ¿ A = two rt. A. Draw С E...

...of those numbers, say Sj, ¿2, . . . ^. These divisors necessarily * Take as an example the theorem that the sum of the three angles of a triangle is equal to rightangles : as soon as by a stroke of the imagination a line is conceived as drawn from one angle...