Question 310887
{{{y=3x+1}}}
Perpendicular lines have slopes that are negative reciprocals. 
{{{m1*m2=-1}}}
{{{3*m2=-1}}}
{{{m2=-1/3}}}
The first line crosses the x-axis ({{{y=0}}}) when {{{x=-1/3}}}.
Use the point slope form of a line,
{{{y-yp=m(x-xp)}}}
{{{y-0=-(1/3)(x-(-1/3))}}}
{{{highlight_green(y= -(1/3)x-1/9) }}}
{{{ graph( 300, 300, -3, 3, -3, 3, -(1/3)x-1/9, 3x+1) }}}