Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 33
es formed outside the triangle are equal to the two inside at A and C;and the three angles at B are equal to the three angles of the triangle, andtheir sum is equal to two right angles. Therefore, the sum of the three anglesof a triangle is equal to two right angles. On one side of a triangle (Fig.…
Mechanical drawing
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