Question

Two lines have equations y + m1x + c1 and y + m2x +c2, m1m2 = -1. Prove that the lines are perpendicular.

Answer 1

Y=mx+b
m=slope

perpendicular lines have slopes that multiply to get -1

the slopes are

for $y=m_1x+c_1$ and $y=m_2x+c_2$, the slope are $m_1 \space\ and \space\ m_2$
since their product is -1, the lines are perpendicular