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The area of an acute triangle ABC is Del...

The area of an acute triangle ABC is `Delta`, the area of its pedal triangle is 'p' , where `cos B=(2p)/(Delta)` and `sin B=(2sqrt(3)p)/(Delta)`. The value of `8(cos^(2)A cos B+cos^(2)C)` is

A

1

B

2

C

3

D

none of these

Text Solution

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The correct Answer is:
To solve the problem, we need to find the value of \( 8(\cos^2 A \cos B + \cos^2 C) \) given the conditions about the triangle ABC. ### Step-by-Step Solution: 1. **Understanding the Given Information**: We have the following: - Area of triangle ABC: \( \Delta \) - Area of the pedal triangle: \( p \) - \( \cos B = \frac{2p}{\Delta} \) - \( \sin B = \frac{2\sqrt{3}p}{\Delta} \) 2. **Using the Pythagorean Identity**: From the identity \( \cos^2 B + \sin^2 B = 1 \): \[ \left(\frac{2p}{\Delta}\right)^2 + \left(\frac{2\sqrt{3}p}{\Delta}\right)^2 = 1 \] Simplifying this: \[ \frac{4p^2}{\Delta^2} + \frac{12p^2}{\Delta^2} = 1 \] \[ \frac{16p^2}{\Delta^2} = 1 \] \[ 16p^2 = \Delta^2 \implies \Delta = 4p \] 3. **Finding \( \frac{p}{\Delta} \)**: \[ \frac{p}{\Delta} = \frac{p}{4p} = \frac{1}{4} \] 4. **Using the Relationship of Areas**: We have established that \( \Delta = 4p \). Now we can express \( \cos B \) and \( \sin B \) in terms of \( p \): \[ \cos B = \frac{2p}{4p} = \frac{1}{2} \] \[ \sin B = \frac{2\sqrt{3}p}{4p} = \frac{\sqrt{3}}{2} \] 5. **Identifying Angles**: Since \( \cos B = \frac{1}{2} \) and \( \sin B = \frac{\sqrt{3}}{2} \), we can conclude that: \[ B = 60^\circ \] 6. **Equilateral Triangle**: Given that \( B = 60^\circ \) and the triangle is acute, we can deduce that \( A = 60^\circ \) and \( C = 60^\circ \) as well. Thus, triangle ABC is equilateral. 7. **Calculating \( 8(\cos^2 A \cos B + \cos^2 C) \)**: Since \( A = B = C = 60^\circ \): \[ \cos A = \cos B = \cos C = \frac{1}{2} \] Therefore: \[ \cos^2 A = \cos^2 B = \cos^2 C = \left(\frac{1}{2}\right)^2 = \frac{1}{4} \] Now substituting into the expression: \[ 8\left(\cos^2 A \cos B + \cos^2 C\right) = 8\left(\frac{1}{4} \cdot \frac{1}{2} + \frac{1}{4}\right) \] \[ = 8\left(\frac{1}{8} + \frac{1}{4}\right) = 8\left(\frac{1}{8} + \frac{2}{8}\right) = 8\left(\frac{3}{8}\right) = 3 \] ### Final Answer: The value of \( 8(\cos^2 A \cos B + \cos^2 C) \) is \( 3 \).

To solve the problem, we need to find the value of \( 8(\cos^2 A \cos B + \cos^2 C) \) given the conditions about the triangle ABC. ### Step-by-Step Solution: 1. **Understanding the Given Information**: We have the following: - Area of triangle ABC: \( \Delta \) - Area of the pedal triangle: \( p \) ...
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