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