Use a calculator to approximate each real number value. (Be sure the calculator is in radian mode.) 
y = cos⁻¹ (―0.32647891)

Key Concepts

Inverse Trigonometric Functions

Inverse trigonometric functions, such as cos⁻¹ (arccosine), are used to find the angle whose cosine is a given value. These functions are essential for solving problems where the angle is unknown, and they return values within specific ranges, typically between 0 and π for arccosine.

Radian Measure

Radian measure is a way of measuring angles based on the radius of a circle. One radian is the angle formed when the arc length is equal to the radius. Understanding radian measure is crucial when using calculators, as many trigonometric functions are often computed in radians rather than degrees.

Calculator Settings

Using a calculator in the correct mode (radian or degree) is vital for accurate trigonometric calculations. When solving problems involving inverse trigonometric functions, ensuring the calculator is set to radian mode will yield the correct angle in radians, which is necessary for further calculations or applications.