In $\triangle A B C, \frac{r_1-r}{a}+\frac{r_2-r}{b}+\frac{r_3-r}{c}=$

In $\triangle A B C, \frac{r_1-r}{a}+\frac{r_2-r}{b}+\frac{r_3-r}{c}=$
  1. $\frac{r_1+r_2+r_3}{s}$
  2. $\frac{r_1+r_2+r_3}{2 s}$
  3. $\frac{r_1+r_2+r_3}{2}$
  4. $\frac{r_1+r_2+r_3}{3 s}$

Solution

In $\triangle A B C$, $ \begin{aligned} & \frac{r_1-r}{a}+\frac{r_2-r}{b}+\frac{r_3-r}{c} \\ & =\frac{\frac{\Delta}{s-a}-\frac{\Delta}{s}}{a}+\frac{\frac{\Delta}{s-b}-\frac{\Delta}{s}}{b}+\frac{\frac{\Delta}{s-c}-\frac{\Delta}{s}}{c} \\ & \therefore \quad\left[r_1=\frac{\Delta}{s-a} r_2=\frac{\Delta}{s-b} r_3=\frac{\Delta}{s-c} \text { and } r=\frac{\Delta}{s}\right] \\ & =\frac{\Delta(s-s+a)}{a s(s-a)}+\frac{\Delta(s-s+b)}{b s(s-b)}+\frac{\Delta(s-s+c)}{c s(s-a)} \\ & =\frac{\Delta}{s-a} \cdot \frac{1}{s}+\frac{\Delta}{s-b} \cdot \frac{1}{s}+\frac{\Delta}{s-c} \cdot \frac{1}{s} \\ & =\frac{r_1}{s}+\frac{r_2}{s}+\frac{r_3}{s}=\frac{r_1+r_2+r_3}{s} \\ & \end{aligned} $

Asked in: AP EAMCET 2018 (23 Apr Shift 1)

Practice more Properties of Triangles questions on Aicharya