Find the ratio in which the point (−3, k) divides the join of A(−5, −4) and B(−2, 3). Also, find the value of k.
Let the point P(−3, k) divide the line AB in the ratio s : 1.
Then, by the section formula:
$x=\frac{m x_{2}+n x_{1}}{m+n}, y=\frac{m y_{2}+n y_{1}}{m+n}$
The coordinates of $P$ are $(-3, k)$.
$-3=\frac{-2 s-5}{s+1}, k=\frac{3 s-4}{s+1}$
$\Rightarrow-3 s-3=-2 s-5, k(s+1)=3 s-4$
$\Rightarrow-3 s+2 s=-5+3, k(s+1)=3 s-4$
$\Rightarrow-s=-2, k(s+1)=3 s-4$
$\Rightarrow s=2, k(s+1)=3 s-4$
Therefore, the point $P$ divides the line $A B$ in the ratio $2: 1$.
Now, putting the value of $s$ in the equation $k(s+1)=3 s-4$, we get:
$k(2+1)=3(2)-4$
$\Rightarrow 3 k=6-4$
$\Rightarrow 3 k=2 \Rightarrow k=\frac{2}{3}$
Therefore, the value of $k=\frac{2}{3}$
That is, the coordinates of $P$ are $\left(-3, \frac{2}{3}\right)$.