Wentworth, G. A. (George Albert), 1835-1906 · Boston, Ginn & company · leaf 49
the acute angle; but if an acuteangle be added to or subtracted from 90° or 270°, the functionsof the resulting angle are equal in absolute value to the co-namedfunctions of the acute angle. It is evident from the formulas for (180° — x) that, A given value of a sine determines two supplementary… … § 29. Angles whose Difference is 90°. The general form of two such angles is x and 90° -f x, andthey must lie in adjoining quadrants. The relations between their functions were found in§ 28, but only for the case whenx is acute. These relations, how-ever, may be shown to hold truefor all values of…
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