Plane trigonometry, by S.L. Loney.

CHAPTER II.

TRIGONOMETRICAL RATIOS FOR ANGLES LESS THAN
A RIGHT ANGLE.
23. IN the present chapter we shall only consider
angles which are less than a right angle.
Let a revolving line OP start from OA and revolve
into the position OP, thus tracing out
the angle AOP. p
In the revolving line take any
point P and draw PM perpendicular
to the initial line OA. o A
In the triangle MOP, OP is the
hypothenuse, PM is the perpendicular, and OM is the base.
The trigonometrical ratios, or functions, of the angle
A OP are defined as follows;
MP Perp.
O' i.e. H-, is called the Sine of the angle AOP;
OM Base
OP' iHyp. '
o i.e. Hyp.',,, Cosine,
MP. Perp.
OHM1' e' Base',, Tangent,,
OM. Base
MP ) Zem Perp.?,, Cotangent,,,
OP. Hyp.
OP.Perp. Cosecant
MP' Perp. '
OP i. Hyp.
OM'.e. Base,, Secant,,
~' ~Base' " " " 2-2
2-2