[tex]\bf \begin{array}{lllll}
&x_1&y_1&x_2&y_2\\
% (a,b)
&({{ 3}}\quad ,&{{ 7}})\quad
% (c,d)
&({{ -1}}\quad ,&{{ -1}})
\end{array}
\\\\\\
% slope = m
slope = {{ m}}= \cfrac{rise}{run} \implies
\cfrac{{{ y_2}}-{{ y_1}}}{{{ x_2}}-{{ x_1}}}\implies \cfrac{-1-7}{-1-3}\implies \cfrac{-8}{-4}\implies 2[/tex]
[tex]\bf y-{{ y_1}}={{ m}}(x-{{ x_1}})\implies y-7=2(x-3)\\
\left. \qquad \right. \uparrow\\
\textit{point-slope form}
\\\\\\
y-7=2x-6\implies y=2x+1[/tex]
