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{{ printedBook.courseTrack.name }} {{ printedBook.name }} The given line $y=21 x+3,$ which is written in slope-intercept form, has a slope of $21 .$ Let's remember the definition of the slope of a line. $m=runrise $ For a slope of $21 ,$ for every $2$ units we move right the line moves up $1$ unit. Recall that the slopes of perpendicular lines are opposite reciprocals. Therefore, a line which is perpendicular to the given line has a slope of $-2.$ We will look for lines such that for every unit we move to the right, the line moves $2$ unit down.

From the diagram above, we can see that only line $b$ has a slope of $-2.$ Therefore, line $b$ is the only perpendicular line to $y=21 x+3.$Let's graph both lines, $y=21 x+3$ and line $b,$ on the same coordinate plane.