# Discovering Trigonometric Ratios (Sine, Cosine, Tangent)

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Common Core Standards
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712 KB|5 pages
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This is an introductory exploration of the three trigonometric ratios: sine, cosine, and tangent. Students draw a 20, 70, 90 degree triangle. Using the 20 degree angle as reference angle, they are asked to find ratios of different sides. They are unknowingly finding the ratios for sine, cosine, and tangent for a 20 degree angle. Before doing the activity, I tell them to round to their answers to the nearest ten-thousandth. I tell them that whoever is the closest to my answer for each of the categories in the table on the second page gets an extra credit point or a prize. When students are done with their calculations, they can write what they got on the table on the second page. I project it on the board so that everyone can see each others results. After doing the activity and choosing winners, I explain what each of the ratios represent and name them sine, cosine, and tangent. I also explain to them that everyones triangles were different sizes but the ratios should be the same. It leads to many rich conversations. You can talk about what happens if you change your reference angle to the 70 or 90 degree angle.

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5 pages
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