Question:
In what ratio does the line x − y − 2 = 0 divide the line segment joining the points A(3, −1) and B(8, 9)?
Solution:
Let the line x − y − 2 = 0 divide the line segment joining the points A(3, −1) and B(8, 9) in the ratio k : 1 at P.
Then, the coordinates of P are
$P\left(\frac{8 k+3}{k+1}, \frac{9 k-1}{k+1}\right)$
Since, P lies on the line x − y − 2 = 0, we have:
$\left(\frac{8 k+3}{k+1}\right)-\left(\frac{9 k-1}{k+1}\right)-2=0$
$\Rightarrow 8 k+3-9 k+1-2 k-2=0$
$\Rightarrow 8 k-9 k-2 k+3+1-2=0$
$\Rightarrow-3 k+2=0$
$\Rightarrow-3 k=-2$
$\Rightarrow k=\frac{2}{3}$
So, the required ratio is $\frac{2}{3}: 1$, which is equal to $2: 3$.