Question

Find the value of $p$ for which the points $(-1,3)$, $(2,p)$ and $(5,-1)$ are collinear.

Answer 1

$\frac{p-3}{2-(-1)}=\frac{-1-p}{5-2}$

$\frac{p-3}{3}=\frac{-1-p}{3}$

$p-3=-1-p$

$2p=3-1$

$2p=2$

$p=1$.