Chapter 7: Q. 2 (page 500)

Find the exact value of the expression:
$\cos 285 ° \cdot \cos 195 °$

Short Answer

Expert verified

The exact value is $0$ .

Step by step solution

Step 1. Given information.

Consider the given question,

$\cos 285 ° \cdot \cos 195 °$

We know $\cos a \cdot \cos b = \frac{1}{2} [\cos (a - b) + \cos (a + b)]$ .

Using the formula, we get,

$\cos 285 ° \cdot \cos 195 ° = \frac{1}{2} [\cos (285 - 195) + \cos (285 + 195)]$

Step 2. Simplify the equation.

Continuing the above equation,

\cos 285 ° \cdot \cos 195 ° = \frac{1}{2} [\cos (120 °) + \cos (480 °)] \cos 285 ° \cdot \cos 195 ° = \frac{1}{2} [- \frac{1}{2} + (- \frac{1}{2})] \cos 285 ° \cdot \cos 195 ° = 0

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Find the exact value of the expression:
$\cos 285 ° \cdot \cos 195 °$

Short Answer

Step by step solution

Step 1. Given information.

Step 2. Simplify the equation.

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Find the exact value of the expression:cos285°·cos195°

Short Answer

Step by step solution

Step 1. Given information.

Step 2. Simplify the equation.

One App. One Place for Learning.

Most popular questions from this chapter

Recommended explanations on Math Textbooks

Geometry

Calculus

Applied Mathematics

Mechanics Maths

Pure Maths

Statistics

Study anywhere. Anytime. Across all devices.

Find the exact value of the expression:
$\cos 285 ° \cdot \cos 195 °$