Lesson plan

Understand how triangle similarity leads to the definitions of trigonometric ratios

teaches Common Core State Standards CCSS.Math.Content.HSG-SRT.C.6 http://corestandards.org/Math/Content/HSG/SRT/C/6

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Big Ideas: The values of trigonometric functions come from special relationships that occur between the side lengths and angle measures. The value of trigonometric functions of specific angle measures stay the same even when the side lengths are multiplied by a scale factor. After students have learned the basic trigonometric functions, this lesson will help students to understand how the ratios of side lengths relate to the angle measure used in the trigonometric functions. This lesson will also allow students to understand that similar triangles have equal trigonometric function ratios. Vocabulary: similar, scale factor, ratios, trigonometric functions Special Materials: Protractor and/or compass and ruler to draw and measure right triangles