Question:

In a triangle \( ABC \), the identity holds: \[ s \left( \frac{r_1 - r}{a} + \frac{r_2 - r}{b} + \frac{r_3 - r}{c} \right) = ? \]

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Familiarity with inradius and exradius identities is essential for advanced triangle geometry problems.
Updated On: May 17, 2025
  • \( \frac{1}{r_1} + \frac{1}{r_2} + \frac{1}{r_3} \)
  • \( r_1 + r_2 + r_3 \)
  • \( r_1 r_2 r_3 \)
  • \( \frac{1}{r_1} + \frac{1}{r_2} + \frac{1}{r_3} \quad \text{(written again)} \)
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The Correct Option is B

Solution and Explanation

This identity relates the inradius \( r \), the exradii \( r_1, r_2, r_3 \), and the triangle's side lengths. From known triangle geometry identities: \[ s \left( \frac{r_1 - r}{a} + \frac{r_2 - r}{b} + \frac{r_3 - r}{c} \right) = r_1 + r_2 + r_3 - 3r \] But it turns out the original expression actually simplifies as: \[ s \left( \frac{r_1 - r}{a} + \frac{r_2 - r}{b} + \frac{r_3 - r}{c} \right) = r_1 + r_2 + r_3 \]
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