Page 35 - Calculus Demystified

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y CHAPTER 1 Basics

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x

Fig. 1.29

y

3

x

Fig. 1.30

EXAMPLE 1.17
Several anglesare sketched in Fig. 1.31, and both their radian and degree
measures given.

If θ is an angle, let (x, y) be the coordinates of the terminal point of the corre-
sponding radius (called the terminal radius) on the unit circle. We call P = (x, y)
the terminal point corresponding to θ. Look at Fig. 1.32. The number y is called the
sine of θ and is written sin θ. The number x is called the cosine of θ and is written
cos θ.
Since (cos θ, sin θ) are coordinates of a point on the unit circle, the following
two fundamental properties are immediate:

(1) For any number θ,
2
2
(sin θ) + (cos θ) = 1.