9.9 Intro to Trig
Goal: Understand three basic trig relationships.
Trigonometry
Derived from ancient Greek language and means measurement of triangles.
Use to measure objects too big or too far to measure by conventional means.
Examples of measures – distance to stars, heights of tall structures (like
pyramids).
Three Basic Ratios
Sine (sin) – pronounced “sign” not “sin”
Cosine (cos) – pronounced “co-sign”
Tangent (tan)
How is this true?
Read the first few pages of this document for a better understanding of
the role similar triangles play in determining the trig ratios.
Trig Ratios & Special Right
Triangles
Using the figure above and the three basic ratios presented
in Slide 3, copy and complete the table on the next slide.
Trig Ratios for Special Angles
θ = 30°
Sin θ
Cos θ
Tan θ
θ = 60°
θ = 45°
Using Your Calculator
• To set the mode, press the mode key. Scroll down to radian/degree and highlight
degree. Press enter. Then press 2nd quit to exit the mode menu.
• Graphing calculators follow the second keystroke sequence (i.e., SIN 74 ENTER)
More About Using Your Calc
The SIN, COS, and TAN keys are used to find the
ratio when you know the angle measure.
To find an angle given the trig ratio, use the SIN-1,
COS-1, and TAN-1 keys (2nd and then SIN, COS, or
TAN).
Homework
Make sure GSP is complete. All questions should be
answered.
“Chapter 7: Right Triangles” worksheet “classwork”