Explanation
Three or more points are collinear if the slope of any two pairs of points is the same
From the question.
Thus, for line AB
[tex]\begin{gathered} \text{slope of AB is given by} \\ \text{slope AB=}\frac{rise}{run}=\frac{change\text{ in y}}{change\text{ in x}}=\frac{3}{1}=3 \end{gathered}[/tex]
Similarly, the slope of DC will be equal to that of AB because they are collinear
Thus
[tex]\text{slope of DC=3}[/tex]
