Trigonometric functions describe the relationship between angles and sides in triangles. The three most common of these trigonometric functions are sine, cosine, and tangent. Lesser commonly used trigonometric function include secant, cosecant, and cotangent.
In the beginning of this chapter we are going to focus on using the sine, cosine, and tangent ratios in right triangles. In a right triangle the sine for an acute angle is defined as the ratio of the lengths of the opposite side and the hypotenuse. Cosine is defined as the ratio of the lengths of the adjacent side and the hypotenuse. Tangent of an acute angle is the ratio of the lengths of the opposite side and the adjacent side.
Sine, cosine, and tangent each have an inverse function. These are called inverse sine, inverse cosine, and inverse tangent.
Later in the chapter we are going to introduce the unit circle and use it as an alternative way to define the trigonometric functions. In doing so a new angle unit called the radian will be introduced.
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