Math Problem Statement

Question 7(Multiple Choice Worth 3 points) (05.05 MC)

Given x equals pi over 6 comma what is the exact value of cos(2π − x)?

one half negative one half radical 3 over 2 negative radical 3 over 2

Solution

We are given that x=π6x = \frac{\pi}{6}, and we are asked to find the exact value of cos(2πx)\cos(2\pi - x).

Step 1: Substitute the given value of xx into the expression.

We know that x=π6x = \frac{\pi}{6}, so we substitute it into cos(2πx)\cos(2\pi - x): cos(2ππ6)\cos(2\pi - \frac{\pi}{6})

Step 2: Simplify the angle.

We simplify 2ππ62\pi - \frac{\pi}{6}. First, express 2π2\pi with a common denominator: 2π=12π62\pi = \frac{12\pi}{6} Now subtract π6\frac{\pi}{6} from 12π6\frac{12\pi}{6}: 2ππ6=12π6π6=11π62\pi - \frac{\pi}{6} = \frac{12\pi}{6} - \frac{\pi}{6} = \frac{11\pi}{6}

Step 3: Find the cosine of the angle 11π6\frac{11\pi}{6}.

The angle 11π6\frac{11\pi}{6} lies in the fourth quadrant, where cosine is positive. To find the cosine, we calculate the reference angle. The reference angle is: 2π11π6=π62\pi - \frac{11\pi}{6} = \frac{\pi}{6} We know that cos(π6)=32\cos(\frac{\pi}{6}) = \frac{\sqrt{3}}{2}.

Since 11π6\frac{11\pi}{6} is in the fourth quadrant, where cosine is positive, we have: cos(11π6)=32\cos\left(\frac{11\pi}{6}\right) = \frac{\sqrt{3}}{2}

Final Answer:

The exact value of cos(2πx)\cos(2\pi - x) is 32\frac{\sqrt{3}}{2}.

Thus, the correct answer is 32\frac{\sqrt{3}}{2}, which corresponds to: Radical 3 over 2.


Would you like more details or have any further questions on this? Here are some related questions to explore:

  1. How does the cosine function behave in different quadrants?
  2. What is the reference angle for angles in the second and third quadrants?
  3. Can you derive the cosine and sine of common angles like π3\frac{\pi}{3}, π4\frac{\pi}{4}, etc.?
  4. How do you apply trigonometric identities to simplify expressions?
  5. How do you solve for exact values of trigonometric functions at non-standard angles?

Tip: Remember that the cosine function is positive in the first and fourth quadrants and negative in the second and third quadrants.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Cosine Function
Quadrants of the Unit Circle

Formulas

cos(2π − x) = cos(2π − x)

Theorems

Cosine function behavior in different quadrants
Reference angle in trigonometry

Suitable Grade Level

Grades 9-12