2.3: Trigonometric Patterns
This activity is intended to supplement Trigonometry, Chapter 1, Lesson 8.
ID: 12434
Time required: 15 minutes
Activity Overview
Students will use the unit circle to examine patterns in the six trigonometric functions.
Topic: Trigonometry
 Unit Circle
 Right Triangle Trigonometry
Teacher Preparation and Notes
 The angle measures will vary from the exact values in the answer tables due to Cabri Jr. only being able to measure coordinates to one decimal place. Make students aware that they may need to use the closest angle measure possible for some values.
 The questions in the document are starting points for discussions about the patterns in the values of trig functions. Teachers should be prepared to discuss patterns beyond the ones in the document.
 To download Cabri Jr, go to http://www.education.ti.com/calculators/downloads/US/Software/Detail?id=258#.
 To download the calculator file, go to http://www.education.ti.com/calculators/downloads/US/Activities/Detail?id=12434 and select UNITC.
Associated Materials
 Student Worksheet: Trigonometric Patterns http://www.ck12.org/flexr/chapter/9699, scroll down to the third activity.
 Cabri Jr. Application
 UNITC.8xv
Trigonometric Patterns
Students will move the triangle on the unit circle to find the angle measures listed in the table on the student worksheet. Students will record the values and then answer questions about patterns in the results. Because the Cabri Jr. file only measures the angle less than
Students can write the ratios on their worksheet and then use the Home screen to do their calculations.
Note that due to rounding in Cabri Jr., the answers are approximate, not exact.
Discussion Questions

What happens at
90∘ ,180∘ ,270∘ , and360∘ ?  Why is the tangent function undefined for some angle measures?
Extension – Patterns in reciprocal functions
In this problem, students will repeat the activity for the cotrigonometric functions. Students should notice that these functions are the reciprocals of the functions from the first part of the activity by looking at the given formulas. This will help them in calculating these functions because they can use simply find the reciprocals on the Home screen instead of finding new ratios.
Discussion Questions
 Are any of the functions undefined? For what values?
Do any of the patterns match the patterns from the functions in the activity?
Solutions






0.5  0.866  0.577 

0.707  0.707  1 

0.866  0.5  1.732 

1  0  Undefined 

0.866  0.5  1.732 

0.707  0.707  1 

0.5  0.866  0.577 

0  1  0 

0.5  0.866  0.577 

0.707  0.707  1 

0.866  0.5  1.732 

1  0  Undefined 

0.866  0.5  1.732 

0.707  0.707  1 

0.5  0.866  0.577 

0  1  0 
1.
2.
3. Positive
Negative
4.
5. Possible response:
6.
7. Possible response:
8. Answers will vary. Sample response: The values in the first quadrant are repeated in the other quadrants, but have different signs.
9. Answers will vary. Sample response: The values of sine and cosine switch within a quadrant, such as
Extension






1.155  2  1.732 

1.414  1.414  1 

2  1.155  0.577 

Undefined  1  0 

2  1.155  1.732 

1.414  1.414  1 

1.155  2  1.732 

1  Undefined  Undefined 

1.155  2  1.732 
\begin{align*}225^\circ\end{align*}  1.414  1.414  1 
\begin{align*}240^\circ\end{align*}  2  1.155  0.577 
\begin{align*}270^\circ\end{align*}  Undefined  1  0 
\begin{align*}300^\circ\end{align*}  2  1.155  0.577 
\begin{align*}315^\circ\end{align*}  1.414  1.414  1 
\begin{align*}330^\circ\end{align*}  1.144  2  1.732 
\begin{align*}360^\circ\end{align*}  1  Undefined  Undefined 
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