Answer
$\color{blue}{y=\dfrac{1}{2}x}$
Work Step by Step
RECALL:
$y=mx+b$, where $m=slope$ and $b$ = y-intercept.
The given line has a y-intercept of $0$, so its tentative equation is:
$y=mx + 0
\\y=mx$
To find the value of $m$, substitute the x and y values of the point $(2, 1)$ into the tentative equation to obtain:
$y=mx
\\1 = m(2)
\\1=2m
\\\frac{1}{2}=m$
Thus, the equation of the line is $\color{blue}{y=\dfrac{1}{2}x}$.
