# Section 7-3 The Sine and Cosine Functions Objective: To use the definitions of sine and cosine to find values of these functions and to solve simple trigonometric.

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Section 7-3 The Sine and Cosine Functions Objective: To use the definitions of sine and cosine to find values of these functions and to solve simple trigonometric equations.

Review topics Draw a circle: Label each quadrants as 1-4 Note the positive or negative x and y values in each quadrant

http://mathrescue.blogspot.com/201 2/08/trigonometry-evaluating-base- angles.html

Trig Trick!

Draw a UC Identify the quadrants; what is the sign of (x,y) in each quadrant?

Review of geometry concepts Given a right triangle, do you remember the definition of sin  and cos  ?

An angle in the standard position

We can study the same angle… It is in the standard position. Its vertex is on point (0,0). It is on the coordinate system.

Now what if the same triangle was within a circle on

Sine and Cosine Functions –We define the sine of θ, denoted sin θ, by: We define the cosine of θ, denoted cos θ, by:

What if r=1 If r=1 what does sin θ and cos θ equal to? sin θ=y cos θ=x

The Unit Circle The circle of radius 1 is called the unit circle.

We can determine the value of many angles on the unit circle. Find A.) sin 90° B.) sin 450° C.) cos (-π)

Example 1 If the terminal ray of an angle θ in standard position passes through (-3, 2), find sin θ and cos θ. Solution: On a grid, locate (-3,2) Use this point to draw a right triangle, where one side is on the x-axis, and the hypotenuse is line segment between (-3,2) and (0,0).

Example 2 Given θ is a 4 th quadrant angle Find cos .

Unit Circle The circle x 2 + y 2 = 1 has radius 1 and is therefore called the unit circle. This circle is the easiest one with which to work because, as the diagram shows, sin θ and cos θ are simply the y- and x-coordinates of the point where the terminal ray of θ intersects the circle. Sin θ = y / r = y / 1 = y Cos θ = x / r = x / 1 = x When a circle is used to define the trigonometric functions, they are sometimes called circular functions.

Example 4 Solve sin θ = 1 for θ in degrees.

Repeating Sin and Cos Values Sin (θ + 360°) = sin θ Cos (θ + 360°) = cos θ Sin (θ + 2π) = sin θ Cos (θ + 2π) = cos θ Sin (θ + 360°n) = sin θ Cos (θ + 360°n) = cos θ Sin (θ + 2πn) = sin θ Cos (θ + 2πn) = cos θ

Homework sec 7.3 written exercises Day 1: Problems # 1-16 All Day 2 #17-28, 33-42 ALL

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