Question

By using slopes, show that the following points are collinear
$D(5,1)$, $E(1,-1)$, $R(11,4)$

Answer 1

Slope of DE$=\frac{-1-1}{1-5}=\frac{-2}{-4}$

$=\frac{1}{2}$

Slope of ER$=\frac{4-(-1)}{11-1}$

$=\frac{5}{10}=\frac{1}{2}$

$\therefore$ Slope of DE$=$slope of ER

$\therefore$ Points are collinear.