Find the exact value of the trigonometric expression without the use of a calculator. 5л 5л (3) 12 4 12 os COS 5л 12 COS COS + sin + sin 5л 12 sin 4 ... sin 4 4 Simplify your answer, including any radicals. Use integers or fractions for any numbers in the expression.

Trigonometry (11th Edition)
11th Edition
ISBN:9780134217437
Author:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Publisher:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Chapter1: Trigonometric Functions
Section: Chapter Questions
Problem 1RE: 1. Give the measures of the complement and the supplement of an angle measuring 35°.
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**Title: Calculation of Trigonometric Expression**

**Objective:**
Find the exact value of the trigonometric expression without the use of a calculator.

**Expression:**
\[ \cos\left(\frac{5\pi}{12}\right)\cos\left(\frac{\pi}{4}\right) + \sin\left(\frac{5\pi}{12}\right)\sin\left(\frac{\pi}{4}\right) \]

**Step-by-Step Solution:**

1. **Identify the trigonometric identity:**
   The given expression is in the form of the cosine addition formula:
   \[
   \cos(A) \cos(B) + \sin(A) \sin(B) = \cos(A - B)
   \]

2. **Apply the identity to the given expression:**
   \[
   \cos\left(\frac{5\pi}{12}\right)\cos\left(\frac{\pi}{4}\right) + \sin\left(\frac{5\pi}{12}\right)\sin\left(\frac{\pi}{4}\right) = \cos\left(\frac{5\pi}{12} - \frac{\pi}{4}\right)
   \]

3. **Simplify the argument of the cosine function:**
   \[
   \frac{5\pi}{12} - \frac{\pi}{4} = \frac{5\pi}{12} - \frac{3\pi}{12} = \frac{2\pi}{12} = \frac{\pi}{6}
   \]

4. **Find the exact value:**
   \[
   \cos\left(\frac{\pi}{6}\right) = \frac{\sqrt{3}}{2}
   \]

**Conclusion:**
The exact value of the trigonometric expression is:
\[ \boxed{\frac{\sqrt{3}}{2}} \]

---

(Simplify your answer, including any radicals. Use integers or fractions for any numbers in the expression.)
Transcribed Image Text:--- **Title: Calculation of Trigonometric Expression** **Objective:** Find the exact value of the trigonometric expression without the use of a calculator. **Expression:** \[ \cos\left(\frac{5\pi}{12}\right)\cos\left(\frac{\pi}{4}\right) + \sin\left(\frac{5\pi}{12}\right)\sin\left(\frac{\pi}{4}\right) \] **Step-by-Step Solution:** 1. **Identify the trigonometric identity:** The given expression is in the form of the cosine addition formula: \[ \cos(A) \cos(B) + \sin(A) \sin(B) = \cos(A - B) \] 2. **Apply the identity to the given expression:** \[ \cos\left(\frac{5\pi}{12}\right)\cos\left(\frac{\pi}{4}\right) + \sin\left(\frac{5\pi}{12}\right)\sin\left(\frac{\pi}{4}\right) = \cos\left(\frac{5\pi}{12} - \frac{\pi}{4}\right) \] 3. **Simplify the argument of the cosine function:** \[ \frac{5\pi}{12} - \frac{\pi}{4} = \frac{5\pi}{12} - \frac{3\pi}{12} = \frac{2\pi}{12} = \frac{\pi}{6} \] 4. **Find the exact value:** \[ \cos\left(\frac{\pi}{6}\right) = \frac{\sqrt{3}}{2} \] **Conclusion:** The exact value of the trigonometric expression is: \[ \boxed{\frac{\sqrt{3}}{2}} \] --- (Simplify your answer, including any radicals. Use integers or fractions for any numbers in the expression.)
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