Chapter 2: Problem 62
Evaluate the trigonometric expressions with a calculator. Round your answer to four decimal places. $$ \cos 317^{\circ} $$
Short Answer
Expert verified
0.7571
Step by step solution
01
Understand the Angle
Recognize that the angle is given in degrees, specifically at 317°. This angle is in the fourth quadrant of a unit circle where cosine values are positive.
02
Use the Calculator
Enter 317 degrees into a scientific calculator to find the cosine value. Ensure the calculator is in degree mode (not radians).
03
Record the Calculator Result
The calculator gives the result for \( \cos 317^{\circ} \approx 0.7571 \). Make sure the result is rounded to four decimal places as required.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cosine Function
The cosine function, denoted as \( \cos \), is a fundamental concept in trigonometry. It relates the angle of a right triangle to the ratio of the length of the adjacent side over the hypotenuse. Here are some key points about cosine:
- It's a periodic function with a period of 360 degrees or \( 2\pi \) radians.
- The cosine values range from -1 to 1.
- It is often used to determine the horizontal coordinate of a point on a unit circle for a given angle.
- In the context of a unit circle, cosine represents the x-coordinate of the point where the terminal side of the angle intersects the circle.
Unit Circle
The unit circle is a crucial concept when dealing with trigonometric functions like cosine. It simplifies the visualization of angles and their respective trigonometric ratios.
- A unit circle is a circle with a radius of 1 centered at the origin of a coordinate plane.
- Any angle's terminal side will intersect the circle, providing corresponding coordinates. These coordinates help determine the sine and cosine values.
- For instance, a 317° angle is positioned in the fourth quadrant of a unit circle, where cosine values are positive and sine values are negative.
- This spatial understanding aids in recognizing how angles transform across quadrants and how their trigonometric values change.
Calculator Usage
Using a calculator can greatly simplify the process of finding cosine and other trigonometric values. This process involves several steps:
- First, make sure the calculator is turned on and ready for input.
- Navigate to the trigonometric function buttons, usually labeled as "sin," "cos," and "tan." For our problem, we focus on the "cos" button.
- Input the angle value, which in our example is 317 degrees. Press the "cos" button to calculate the value.
- Lastly, review the result and ensure it aligns with the expected outcome of being in the correct quadrant and sign.
Degree Mode
When using a scientific calculator to evaluate trigonometric functions, setting the calculator to the correct mode is critical to obtain accurate results.
- Calculators typically have two modes for angle input: degree mode and radian mode.
- The exercise specifically deals with degrees, so it is vital to switch the calculator to degree mode to align with this requirement.
- Changing the mode incorrectly can result in significant errors because the outputs will be incorrect for the angle input provided.
- Always double-check that the calculator displays "D" or "Degree" on its screen before beginning any trigonometric calculation involving degrees.