## Intermediate Algebra (12th Edition)

We know that two parallel lines have the same slope ($m_1=m_2$). We also know that perpendicular lines have negative reciprocal slopes ($m_1=-\frac{1}{m_2}$). A line in slope-intercept form has the equation: $y=mx+b$ ($m=slope$, $b=y-intercept$) We put the line equations into slope-intercept form: $4x-3y=8$ $-3y=8-4x$ $y=-8/3+4/3x$ $y=4/3x-8/3$ And: $4y+3x=12$ $4y=-3x+12$ $y=-3/4x+3$ The two slopes ($4/3$ and $-3/4$) are negative reciprocals. Thus the lines are perpendicular.