Use a calculator to find a decimal approximation for each...

Use a calculator to find a decimal approximation for each value. Give as many digits as your calculator displays. Simplify the expression before using the calculator. See Example 7.
$$\cos \left(-15^{\circ}\right)$$

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Key Concepts

Even Function Property

The cosine function is an example of an even function, which means that its value remains unchanged when the angle's sign is reversed. This property, mathematically expressed as cos(–?) = cos(?), is fundamental for simplifying expressions involving cosine, especially when negative angles are present.

Trigonometric Functions

Trigonometric functions, such as cosine, are central to the study of angles and periodic phenomena. They relate angles to ratios in right triangles or points on the unit circle, and understanding these functions is key for solving problems in both pure and applied mathematics.

Angle Measurement in Degrees

Angles can be measured in degrees or radians, and in many practical problems, including this one, degrees are used. Converting or not converting between these units correctly is essential for accurate computation, especially when using a calculator that may be in a specific mode.

Calculator Approximations in Trigonometry

Using a calculator to obtain decimal approximations for trigonometric values is a common technique in mathematics when exact values are complex or not easily determined. Ensuring that the calculator is set to the correct mode (such as degree mode for angle measurements in degrees) is critical for accurate approximation.

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