Define and calculate the cosine of angles in right triangles. Use similarity criteria to generalize the definition of cosine to all angles of the same measure.
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Below is a set of similar right triangles. Find the ratio of the side lengths within each triangle that describe the side adjacent to the marked angle divided by the hypotenuse.
What is the cosine of 0°, 45°, 60°, and 90°?
$${\triangle ABC}$$ is a right triangle. What is the cosine of $${\angle BAC}$$?
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The following resources include problems and activities aligned to the objective of the lesson that can be used to create your own problem set.
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Explain how you know that the following statement is always, sometimes, or never true:
“You can find the cosine of any angle in any triangle by finding the ratio of the length of the adjacent side over the length of the hypotenuse.”
Find the cosine of each angle shown in the diagram below. Then, predict between which two benchmark angle measures the angles fall between based on the cosine.