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Chapter 6: Trigonometry 6

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1 Chapter 6: Trigonometry 6
Chapter 6: Trigonometry 6.4: Trigonometric Functions (Wave Function Approach) Essential Question: What trigonometric function is represented by the x-coordinate and what trigonometric functions is represented by the y-coordinate?

2 6.4: Trigonometric Functions
A note before we begin This PowerPoint is going to deviate significantly from the book. You’re more than welcome to try and interpret the book’s unit circle approach, but the problems assigned can be solved using the wave approach in the following slides. We’ll discuss the unit circle approach Friday, and I want your honest opinion on what you feel is the easier way to understand trig functions.

3 6.4: Trigonometric Functions
The sine curve The sine (sin) curve is a cycle that starts at 0, reaches a max of 1 (at π/2), and a min of -1 (at 3π/2), and cycles every 2π

4 6.4: Trigonometric Functions
The cosine curve The cosine (cos) curve is a cycle that starts at 1, also reaches a max of 1 (at 0), a min of -1 (at π), and cycles every 2π

5 6.4: Trigonometric Functions
The tangent curve tan θ = sin θ / cos θ Where cos θ = 0, the tangent is undefined It spikes up (like x3) in between those undefined points Where sin θ = 0, tan θ = 0 Unlike sin/cos, tan repeats every π radians

6 6.4: Trigonometric Functions
Exact values of trigonometric functions Find the exact values of the sine, cosine, and tangent functions when t = 0, π/2, π, 3π/2 and 2π Sin function Zooming in on the sin graph The sin functions starts at 0, so: sin 0 = 0 sin π/2 = 1 sin π = 0 sin 3π/2 = -1 sin 2π = 0 Cos function Works the same way as the sin function, except cos starts at 1, and begins going down cos 0 = 1 cos π/2 = 0 cos π = -1 cos 3π/2 = 0 cos 2π = 1

7 6.4: Trigonometric Functions
Exact values of trigonometric functions Find the exact values of the sine, cosine, and tangent functions when t = 0, π/2, π, 3π/2 and 2π tan function The first sin/cos columns are from the last slide: t sin t cos t tan t = sin t/cos t 1 π/2 undefined π -1 3π/2

8 6.4: Trigonometric Functions
Trigonometric Ratios of Coterminal Angles Find the sine, cosine, and tangent of 7π/3 7π/3 is greater than 2π, so subtract to give us something to work with 7π/3 – 2π = 7π/3 – 6π/3 = π/3 Personally, I find it easier to think about the waves if you’re thinking in degrees π/3 • 180°/π = 60° → which is one of our special angles The special angles count up… 0, 30, 45, 60, 90, … sin t starts at 0 and counts up… 60 matches up with cos t starts at 1, and counts down tan t = sin t / cos t =

9 6.4: Trigonometric Functions
Hints with angles greater than π (90°) As I mentioned back in section 6.1, the only values you’ll have to memorize are the sin and cosine values. All other trigonometric values can be found based off sin & cos (we’ll explore further in 6.5) This pattern continues until the cycle repeats. Angle 30° 45° 60° 90° 120° 135° 150° 180° 210° cos θ 1 -1 sin θ

10 6.4: Trigonometric Functions
Assignment Page 452 Problems 11-23, (odd) For identifying the quadrants in use (cos x, sin x) to identify the quadrant. For example, let’s look at: #16) 11 [Note: we’re in radian mode in the calculators] cos 11 ≈ sin 11 ≈ We’re at the point (0.0044, ) which is in the 4th quadrant For problems 31 – 53, remember your two numbers to memorize. Leave everything in fraction form (including 0.5 as ½)


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