Cosine function

Definition

The cosine function is a fundamental trigonometric function that relates the angle of a right triangle to the ratio of the length of the adjacent side to the hypotenuse. It is defined for all real numbers and is periodic, meaning it repeats its values in regular intervals. The cosine function plays a crucial role in solving trigonometric equations, particularly when determining unknown angles or sides in geometric contexts.

5 Must Know Facts For Your Next Test

1. The cosine function is usually denoted as cos(θ), where θ represents an angle measured in radians or degrees.
2. The range of the cosine function is between -1 and 1, which means it can never exceed these values.
3. The cosine function is an even function, meaning that cos(-θ) = cos(θ) for any angle θ.
4. One key property of the cosine function is its periodicity: it has a period of 2π radians, meaning cos(θ + 2π) = cos(θ).
5. In solving trigonometric equations, values of θ can be found using the inverse cosine function, denoted as cos^(-1)(x), which helps determine angles from given ratios.

Review Questions

• How does the cosine function relate to solving right triangle problems?
  • The cosine function is essential in solving right triangle problems because it provides a way to relate an angle to the lengths of two sides. Specifically, it allows us to calculate the length of the adjacent side when we know the hypotenuse and the angle or vice versa. By using cos(θ) = adjacent/hypotenuse, we can derive unknown measurements, making it easier to analyze and solve geometric situations.
• Explain how understanding the periodic nature of the cosine function can help in solving trigonometric equations.
  • Understanding that the cosine function is periodic with a period of 2π allows us to find multiple solutions for trigonometric equations within specified intervals. When we solve an equation like cos(θ) = x, recognizing that cos(θ + 2kπ) = x for any integer k means we can generate infinite solutions. This insight is crucial when working with general solutions for angles, as we can represent all possible angles that yield a specific cosine value.
• Evaluate how transformations such as vertical shifts and stretches affect the graph of the cosine function and what implications this has for solving related equations.
  • Transformations like vertical shifts and stretches modify the graph of the cosine function by altering its amplitude and midline position. For instance, if we have a transformed function like y = A * cos(Bθ) + C, where A affects amplitude and C shifts vertically, understanding these changes helps predict how solutions will behave. When solving equations involving transformed cosine functions, it's essential to account for these modifications since they influence where intersections with horizontal lines occur, directly impacting solution sets.

Related terms

sine function: A trigonometric function that relates the angle of a right triangle to the ratio of the length of the opposite side to the hypotenuse.

tangent function: A trigonometric function that relates the angle of a right triangle to the ratio of the length of the opposite side to the adjacent side.

unit circle: A circle with a radius of one centered at the origin of a coordinate system, used to define trigonometric functions such as sine and cosine for all real numbers.