Wentworth, G. A. (George Albert), 1835-1906 · Boston, Ginn & company · leaf 52
cos(180°+a;)cos(270o-y)-sin(180o+^)sin(270o-y). 50. tan x + tan (-y)- tan (180° — y). 51. For what values of x is the expression sin x -f- cos xpositive, and for what values negative ? Represent the resultby a drawing in which the sectors corresponding to the nega-tive values are shaded. 52. Answer… … sin x; hence, FF~ sin x X O-D = sin # cosy.cos#; hence, QQ = cos#X CD = cos#siny. § 31. Functions of the Sum of Two Angles. In a unit circle (Fig. 27) let the angle AOB = x, the angleBOC= y; then the angle A00=x + y. In order to express sin(#-|-y)and cos (x -f- y) in terms of thesines and cosines…
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