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Consider a triangle ABC in which cos A +...

Consider a triangle ABC in which `cos A + cos B + cos C = sqrt(3) "sin"(pi)/(3)`
What is the value of `"sin"(A)/(2)"sin"(B)/(2)"sin"(C)/(2)`?

A

`(1)/(2)`

B

`(1)/(4)`

C

`(1)/(8)`

D

`(1)/(16)`

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The correct Answer is:
To solve the problem, we need to find the value of \( \frac{\sin A}{2} \cdot \frac{\sin B}{2} \cdot \frac{\sin C}{2} \) given that \( \cos A + \cos B + \cos C = \sqrt{3} \sin \left(\frac{\pi}{3}\right) \). ### Step-by-step Solution: 1. **Understanding the Given Equation**: We start with the equation: \[ \cos A + \cos B + \cos C = \sqrt{3} \sin \left(\frac{\pi}{3}\right) \] We know that \( \sin \left(\frac{\pi}{3}\right) = \frac{\sqrt{3}}{2} \), so we can rewrite the equation as: \[ \cos A + \cos B + \cos C = \sqrt{3} \cdot \frac{\sqrt{3}}{2} = \frac{3}{2} \] 2. **Using the Cosine Sum Formula**: We can use the identity for the sum of cosines in a triangle: \[ \cos A + \cos B + \cos C = 1 + \frac{r}{R} \] where \( r \) is the inradius and \( R \) is the circumradius. Setting this equal to \( \frac{3}{2} \): \[ 1 + \frac{r}{R} = \frac{3}{2} \] This implies: \[ \frac{r}{R} = \frac{1}{2} \] 3. **Finding the Value of \( \sin A/2 \cdot \sin B/2 \cdot \sin C/2 \)**: We can use the relationship between the circumradius \( R \) and the angles of the triangle: \[ \sin A + \sin B + \sin C = \frac{r}{R} \cdot 2R = 2r \] Since \( \frac{r}{R} = \frac{1}{2} \), we can use the formula: \[ \sin A \cdot \sin B \cdot \sin C = \frac{r^3}{R^3} \] We are interested in \( \sin \frac{A}{2} \cdot \sin \frac{B}{2} \cdot \sin \frac{C}{2} \). Using the half-angle identity: \[ \sin \frac{A}{2} = \sqrt{\frac{1 - \cos A}{2}}, \quad \sin \frac{B}{2} = \sqrt{\frac{1 - \cos B}{2}}, \quad \sin \frac{C}{2} = \sqrt{\frac{1 - \cos C}{2}} \] Therefore: \[ \sin \frac{A}{2} \cdot \sin \frac{B}{2} \cdot \sin \frac{C}{2} = \sqrt{\frac{(1 - \cos A)(1 - \cos B)(1 - \cos C)}{8}} \] 4. **Calculating the Value**: We know: \[ 1 - \cos A = 1 - \cos B = 1 - \cos C = 1 - \frac{3}{2} + \frac{r}{R} \] Using the previous results, we can simplify: \[ \sin \frac{A}{2} \cdot \sin \frac{B}{2} \cdot \sin \frac{C}{2} = \sqrt{\frac{(1 - \frac{3}{2})(1 - \frac{3}{2})(1 - \frac{3}{2})}{8}} = \sqrt{\frac{(-\frac{1}{2})(-\frac{1}{2})(-\frac{1}{2})}{8}} = \frac{1}{8} \] 5. **Final Result**: Thus, the value of \( \sin \frac{A}{2} \cdot \sin \frac{B}{2} \cdot \sin \frac{C}{2} \) is: \[ \frac{1}{8} \] ### Conclusion: The final answer is: \[ \boxed{\frac{1}{8}} \]

To solve the problem, we need to find the value of \( \frac{\sin A}{2} \cdot \frac{\sin B}{2} \cdot \frac{\sin C}{2} \) given that \( \cos A + \cos B + \cos C = \sqrt{3} \sin \left(\frac{\pi}{3}\right) \). ### Step-by-step Solution: 1. **Understanding the Given Equation**: We start with the equation: \[ \cos A + \cos B + \cos C = \sqrt{3} \sin \left(\frac{\pi}{3}\right) ...
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