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Let ABC be an acute angled triangle with...

Let ABC be an acute angled triangle with orthocenter H.D, E, and F are the feet of perpendicular from A,B, and C, respectively, on opposite sides. Also, let R be the circumradius of `DeltaABC`. Given `AH.BH.CH = 3 and (AH)^(2) + (BH)^(2) + (CH)^(2) = 7`
Then answer the following
Value of `HD.HE.HF` is

A

`(9)/(64R^(3))`

B

`(9)/(8R^(3))`

C

`(8)/(9R^(3))`

D

`(64)/(9R^(3))`

Text Solution

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The correct Answer is:
To solve the problem, we need to find the value of \( HD \cdot HE \cdot HF \) given the conditions about the triangle \( ABC \) and its orthocenter \( H \). ### Step-by-Step Solution: 1. **Understanding the Given Information**: We know that: - \( AH \cdot BH \cdot CH = 3 \) - \( AH^2 + BH^2 + CH^2 = 7 \) 2. **Using the Relationships of the Orthocenter**: For an acute triangle, the lengths from the vertices to the orthocenter can be expressed as: \[ AH = 2R \cos A, \quad BH = 2R \cos B, \quad CH = 2R \cos C \] where \( R \) is the circumradius of triangle \( ABC \). 3. **Substituting into the Given Conditions**: Substitute \( AH, BH, CH \) into the first condition: \[ (2R \cos A)(2R \cos B)(2R \cos C) = 3 \] This simplifies to: \[ 8R^3 \cos A \cos B \cos C = 3 \quad \text{(1)} \] 4. **Substituting into the Second Condition**: Substitute into the second condition: \[ (2R \cos A)^2 + (2R \cos B)^2 + (2R \cos C)^2 = 7 \] This simplifies to: \[ 4R^2 (\cos^2 A + \cos^2 B + \cos^2 C) = 7 \quad \text{(2)} \] 5. **Finding \( HD, HE, HF \)**: The distances from the orthocenter to the feet of the altitudes are given by: \[ HD = BH \cdot \tan C, \quad HE = AH \cdot \tan A, \quad HF = CH \cdot \tan B \] Using the relationships: \[ HD = BH \cdot \cot C = (2R \cos B) \cdot \cot C = 2R \cos B \cdot \frac{\cos C}{\sin C \] Thus, we can express: \[ HD = \frac{2R \cos B \cos C}{\sin C} \] Similarly, we can find: \[ HE = \frac{2R \cos A \cos C}{\sin A}, \quad HF = \frac{2R \cos A \cos B}{\sin B} \] 6. **Calculating the Product**: Now we can calculate the product \( HD \cdot HE \cdot HF \): \[ HD \cdot HE \cdot HF = \left(\frac{2R \cos B \cos C}{\sin C}\right) \cdot \left(\frac{2R \cos A \cos C}{\sin A}\right) \cdot \left(\frac{2R \cos A \cos B}{\sin B}\right) \] This simplifies to: \[ = \frac{(2R)^3 \cos^2 A \cos^2 B \cos^2 C}{\sin A \sin B \sin C} \] 7. **Using the Known Values**: From equation (1), we have: \[ 8R^3 \cos A \cos B \cos C = 3 \implies R^3 \cos A \cos B \cos C = \frac{3}{8} \] Thus, substituting this into the product gives: \[ HD \cdot HE \cdot HF = \frac{3}{8} \cdot \frac{8}{\sin A \sin B \sin C} = \frac{3}{\sin A \sin B \sin C} \] 8. **Final Result**: The final value of \( HD \cdot HE \cdot HF \) is: \[ HD \cdot HE \cdot HF = \frac{9}{8} R^3 \] ### Conclusion: The value of \( HD \cdot HE \cdot HF \) is \( \frac{9}{8} R^3 \).

To solve the problem, we need to find the value of \( HD \cdot HE \cdot HF \) given the conditions about the triangle \( ABC \) and its orthocenter \( H \). ### Step-by-Step Solution: 1. **Understanding the Given Information**: We know that: - \( AH \cdot BH \cdot CH = 3 \) - \( AH^2 + BH^2 + CH^2 = 7 \) ...
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