Answer
$2x-y=2$
Work Step by Step
Using $y-y_1=\dfrac{y_1-y_2}{x_1-x_2}(x-x_1)$ or the two-point form of linear equations, the equation of the line passing through $(
3,4
)$ and $(
5,8
)$ is
\begin{array}{l}\require{cancel}
y-4=\dfrac{4-8}{3-5}(x-3)
\\\\
y-4=\dfrac{-4}{-2}(x-3)
\\\\
y-4=2(x-3)
\\\\
y-4=2x-6
\\\\
-2x+y=-6+4
\\\\
-2x+y=-2
\\\\
2x-y=2
.\end{array}