Spanton, J. Humphrey (John Humphrey) · London, Macmillan and Co., Limited; New York, The Macmillan Company · leaf 26
. 20. :d. Triangles.—The three angles of a triangle con-tain together 180°, or two right angles ; so if twoangles are given, the third angle can always befound. F^or example, if one angle is 70° and theother 30°, the remaining angle must be 80° (Fig. 21).70°+ 30°= 100°.180°- 100° = 80°. The… … b d e Fig. 22. If we multiply the base by half the altitude, we get the areaof a triangle ; or half its base by its altitude will give us thesame result. GEOMETRICAL DEFINITIONS. !3 Triangles of equal bases drawn between parallel lines areequal in area, and lines drawn parallel to their bases at…
Geometrical drawing · Design · Drawing
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