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Let the incircle of DeltaABC touches the...

Let the incircle of `DeltaABC` touches the sides BC, CA, AB at `A_(1), B_(1),C_(1)` respectively. The incircle of `DeltaA_(1)B_(1)C_(1)` touches its sides of `B_(1)C_(1), C_(1)A_(1) and A_(1)B_(1)" at " A_(2), B_(2), C_(2)` respectively and so on.
Q. In `DeltaA_(4)B_(4)C_(4)`, the value of `angleA_(4)` is:

A

`(3pi+A)/(6)`

B

`(3pi-A)/(8)`

C

`(5pi-A)/(16)`

D

`(5pi+A)/(16)`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem step by step, we will analyze the relationship between the angles in the triangles formed by the incircles. ### Step-by-Step Solution: 1. **Understanding the Problem**: We have a triangle \( \Delta ABC \) with an incircle that touches the sides at points \( A_1, B_1, C_1 \). The incircle of triangle \( \Delta A_1B_1C_1 \) touches its sides at points \( A_2, B_2, C_2 \), and this process continues to form triangles \( \Delta A_3B_3C_3 \) and \( \Delta A_4B_4C_4 \). We need to find the value of \( \angle A_4 \). **Hint**: Draw the triangles and their incircles to visualize the problem better. 2. **Identifying Angles in Triangle \( \Delta ABC \)**: The angle \( \angle A \) in triangle \( \Delta ABC \) is given. The angles at the points where the incircle touches the sides can be expressed in terms of \( \angle A \). **Hint**: Remember that the angles formed at the center of the incircle are related to the angles of the triangle. 3. **Finding \( \angle A_1 \)**: From the properties of the incircle, we know: \[ \angle C_1OB_1 = \pi - \angle A \] where \( O \) is the center of the incircle. **Hint**: Use the fact that the angles around point \( O \) sum to \( \pi \). 4. **Finding \( \angle A_2 \)**: In triangle \( \Delta OC_1A_1 \), we can write: \[ \angle C_1OA_1 + 2 \times \angle OA_1C_1 = \pi \] Since \( OC_1 = OA_1 \) (both are inradii), we can conclude: \[ \angle A_1 = \frac{\pi - \angle C_1OA_1}{2} \] **Hint**: Use the equality of angles in isosceles triangles. 5. **Finding \( \angle A_3 \)**: Continuing this process, we find: \[ \angle A_2 = \frac{\pi - \angle A_1}{2} = \frac{\pi - \frac{\pi - \angle A}{2}}{2} = \frac{3\pi + \angle A}{4} \] **Hint**: Substitute the previously found angle into the new equation. 6. **Finding \( \angle A_4 \)**: We can now find \( \angle A_4 \): \[ \angle A_3 = \frac{\pi - \angle A_2}{2} = \frac{\pi - \frac{3\pi + \angle A}{4}}{2} = \frac{5\pi - \angle A}{8} \] Finally, we find \( \angle A_4 \): \[ \angle A_4 = \frac{\pi - \angle A_3}{2} = \frac{\pi - \frac{5\pi - \angle A}{8}}{2} = \frac{5\pi + \angle A}{16} \] **Hint**: Keep track of the fractions carefully as they represent the angles. ### Final Answer: The value of \( \angle A_4 \) is: \[ \angle A_4 = \frac{5\pi + \angle A}{16} \]
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