Page 112 - DMTH401_REAL ANALYSIS

Real Analysis

Notes Figure 9.1

You already know how the trigonometric ratios sin , cos , etc., are defined for an angle 
measured in degrees or radians. We now define sin x, cos x, etc., for x R.

Figure 9.2

2
2
If we put r = 1 in above relation, then we get  = s. Also the equation of circle becomes x + y = 1.
This, as you know, is the Unit Circle. Let C represents this circle with centre O and radius 1.
Suppose the circle meets the x-axis at a point A as shown in the Figure 9.2.

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